Basic operators in java

Types of Operators in Java:

  1. Arithmetic Operators
  2. Bit-wise Operators
  3. Logical Operators
  4. Relational Operators 
  5. Assignment Operators
  6. Misc Operators



Java operator precedence

java order of operations

Arithmetic Operators
  • Arithmetic operators are used in mathematical expressions.
  • Following are the arithmetic operators in java.
  1. +  :  Addition
  2. -   : Subtraction
  3. *  : Multiplication
  4. /   : Division
  5. % : Modulus

Bit wise Operators:

  • Bit wise operators operates on individual bits of operands.
  • Following are the Bit-wise operators in java. 
  • Bitwise operators in java

  1. ~      : Bit wise unary not
  2. &     : Bit wise And
  3. |       : Bit wise OR
  4. ^      : Bit wise Exclusive OR
  5. >>    : Shift Right
  6. >>>  : Shift right zero fill
  7. <<    :Shift left

Logical Operators:

  1. && : Logical AND
  2. ||      : Logical OR
  3. !      : Logical NOT

Relational Operators in java

  1. ==  : Equal to
  2. !=   : Not Equal to
  3. <    : Less Than
  4. >    : Greater Than
  5. >=  : Greater Than or Equal to
  6. <= : Less Than or Equal to

Assignment Operators:

  1. =    : Simple Assignment
  2. +=  : Add and assign
  3. -=   : Subtract and assign
  4. *=   : Multiply and assign
  5. %=  : Modulus and assign
  6. /=    : Divide and assign
  7. &=   : Bit wise AND assignment
  8. |=     : Bit wise assignment OR
  9. ^=    : Bit wise Exclusive OR assignment
  10. >>= : Shift Right assignment
  11. >>>= : Shift right  zero fill assignment
  12. <<=   : Shift left assignment


Misc Operators:

Increment and Decrement operators:
  1. ++ : increment
  2. --   : decrement


Conditional Operator: (?:)

  • Also known as ternary operator
  • Example: int a= 1>2?1:2;

Ternary operator in java


Instanceof Operator
  • Instance of operator is used to test whether that object is belong to that class type or not.
  • If that object belongs to that class it returns true .otherwise it returns false.
  • Instance of operator is also known as comparison operator.because it compares with the instance of type.
Instanceof operator in java

Top 30 frequently asked java interview programs for freshers

Java Example program convert Decimal to Binary

  • On of the way to convert decimal number to its binary representation using the Integer.toBinaryString() method. This method takes an integer as an argument and returns its binary representation as a string. Here is an example:
public static String decimalToBinary(int decimal) {
    return Integer.toBinaryString(decimal);
}

We can call this method and pass a decimal number as an argument, and it will return the binary representation of that number. For example:

int decimal = 10;
String binary = decimalToBinary(decimal);
System.out.println(binary); // Output: 1010

In the above method will return a string representation of the binary number, if we want to have it as an integer you can use Integer.parseInt(binary, 2) to convert it to an int.

Another way to convert a decimal number to its binary representation is by using bit shifting and bitwise operations. You can repeatedly divide the decimal number by 2 and keep track of the remainder. The remainder represents the least significant bit of the binary representation. You can then reverse the order of the remainders to get the binary representation of the decimal number.

In summary, In Java you can use the Integer.toBinaryString() method to convert a decimal number to its binary representation as a string, and you can use Integer.parseInt(binary, 2) to convert it to an int. Also, you can use bit shifting and bitwise operations to convert a decimal number to its binary representation.

Another way to convert a decimal number to its binary representation is by using bit shifting and bitwise operations. 
This method involves repeatedly dividing the decimal number by 2 and keeping track of the remainders. The remainders represent the least significant bits of the binary representation.


public static String decimalToBinaryUsingBitOperation(int decimal) {
    StringBuilder binary = new StringBuilder();
    while (decimal > 0) {
        binary.append(decimal % 2);
        decimal = decimal >> 1;
    }
    return binary.reverse().toString();
}

the function uses a while loop to divide the decimal number by 2 and keep track of the remainders. The remainders are appended to a StringBuilder object. The while loop continues until the decimal number is 0. At the end of the loop, the binary representation of the decimal number is obtained by reversing the order of the remainders using the reverse() method of the StringBuilder. The binary representation is then returned as a string.

This method will also work for negative decimal numbers, but the result will be the two's complement representation of the negative number, it will have a leading 1 in the most significant bit.

It's worth noting that, the above method will return the binary representation as a string, if you want to have it as an integer you can use Integer.parseInt(binary, 2) to convert it to an int.

In summary, there are different ways to convert a decimal number to its binary representation in Java. One way is to use the Integer.toBinaryString() method, another way is by using bit shifting and bitwise operations, this method uses a while loop to repeatedly divide the decimal number by 2 and keep track of the remainders, which represent the binary representation of the decimal number. The result can be returned as a string or as an integer by using the Integer.parseInt(binary, 2)

  • We can convert binary to decimal in three ways
    1.Using Integer.toBinaryString(int num);
    2.Using Stack
    3.Using Custom logic 


1.Write a Java Program to convert decimal to binary in java using Integer.toBinaryString(int num)

  1. import java.util.Scanner;
  2. public class ConvertDecimalToBinary{
  3.  
  4.     /**
  5.      *www.instanceofjava.com
  6.      */
  7.  
  8.  public static void main(String[] args) {
  9.         
  10.  System.out.println("\nBinary representation of 1: ");
  11.  System.out.println(Integer.toBinaryString(1));
  12.  System.out.println("\nBinary representation of 4: ");
  13.  System.out.println(Integer.toBinaryString(4));
  14.  System.out.println("Binary representation of 10: ");
  15.  System.out.println(Integer.toBinaryString(10));
  16.  System.out.println("\nBinary representation of 12: ");
  17.  System.out.println(Integer.toBinaryString(12));
  18.  System.out.println("\nBinary representation of 120: ");
  19.  System.out.println(Integer.toBinaryString(120));
  20.  System.out.println("\nBinary representation of 500: ");
  21.  System.out.println(Integer.toBinaryString(500));

  22. }
  23.  
  24. }





Output:

  1. Binary representation of 1: 
  2. 1
  3. Binary representation of 4: 
  4. 100
  5. Binary representation of 10: 
  6. 1010
  7. Binary representation of 12: 
  8. 1100
  9. Binary representation of 120: 
  10. 1111000
  11. Binary representation of 500: 
  12. 111110100

2.Write a Java Program to convert decimal to binary in java


  1. import java.util.Scanner;
  2. import java.util.Stack;
  3. public class ConvertDecimalToBinary{
  4.  
  5.     /**
  6.      *www.instanceofjava.com
  7.      */
  8.  
  9.  
  10.  public static void main(String[] args) {
  11.         
  12. Scanner in = new Scanner(System.in);
  13.          
  14. // Create Stack object
  15. Stack<Integer> stack = new Stack<Integer>();
  16.      
  17. //Take  User input from keyboard
  18.  System.out.println("Enter decimal number: ");
  19.  int num = in.nextInt();
  20.     
  21. while (num != 0)
  22. {
  23.    int d = num % 2;
  24.    stack.push(d);
  25.    num /= 2;
  26.  
  27.  } 
  28.      
  29.  System.out.print("\nBinary representation is:");
  30.  
  31. while (!(stack.isEmpty() ))
  32.  {
  33.    System.out.print(stack.pop());
  34.  }
  35.         
  36.  
  37. System.out.println();
  38.  
  39. }
  40.  
  41. }
  42.  
  43. }


Output:

  1. Enter decimal number: 
  2. 12
  3.  
  4. Binary representation is:1100

java program convert decimal to binary


3.Write a Java Program to convert decimal to binary in java


  1. import java.util.Scanner;
  2. public class ConvertDecimalToBinary{
  3.  
  4.     /**
  5.      *www.instanceofjava.com
  6.      */
  7.  
  8. public static void convertDeciamlToBinary(int num){
  9.  
  10.   int binary[] = new int[40];
  11.          int index = 0;
  12.  while(num > 0){
  13.            binary[index++] = num%2;
  14.            num = num/2;
  15.  }

  16. for(int i = index-1;i >= 0;i--){
  17.            System.out.print(binary[i]);
  18. }
  19.  
  20. }
  21.  
  22.  public static void main(String[] args) {
  23.         
  24. System.out.println("Binary representation of 1: ");
  25. convertDeciamlToBinary(1);
  26.  
  27. System.out.println("\nBinary representation of 4: ");
  28. convertDeciamlToBinary(4);
  29.  
  30. System.out.println("\nBinary representation of 10: ");
  31. convertDeciamlToBinary(10);
  32.  
  33. System.out.println("\nBinary representation of 12: ");
  34.  convertDeciamlToBinary(12);
  35.  
  36. }
  37.  
  38. }


Output:

  1. Binary representation of 1: 
  2. 1
  3. Binary representation of 4: 
  4. 100
  5. Binary representation of 10: 
  6. 1010
  7. Binary representation of 12: 
  8. 1100

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Java programming interview questions

  1. Print prime numbers? 
  2. What happens if we place return statement in try catch blocks 
  3. Write a java program to convert binary to decimal 
  4. Java Program to convert Decimal to Binary
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  12. Java Program Find Second highest number in an integer array 
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  19. Explain java data types with example programs 
  20. Constructor chaining in java with example programs 
  21. Swap two numbers without using third variable in java 
  22. Find sum of digits in java 
  23. How to create immutable class in java 
  24. AtomicInteger in java 
  25. Check Even or Odd without using modulus and division  
  26. String Reverse Without using String API 
  27. Find Biggest substring in between specified character
  28. Check string is palindrome or not?
  29. Reverse a number in java?
  30. Fibonacci series with Recursive?
  31. Fibonacci series without using Recursive?
  32. Sort the String using string API?
  33. Sort the String without using String API?
  34. what is the difference between method overloading and method overriding?
  35. How to find largest element in an array with index and value ?
  36. Sort integer array using bubble sort in java?
  37. Object Cloning in java example?
  38. Method Overriding in java?
  39. Program for create Singleton class?
  40. Print numbers in pyramid shape?
  41. Check armstrong number or not?
  42. Producer Consumer Problem?
  43. Remove duplicate elements from an array
  44. Convert Byte Array to String
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  47. Multiply 2 Matrices
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  49. Sort ArrayList in descending order
  50. Sort Object Using Comparator
  51. Count Number of Occurrences of character in a String
  52. Can we Overload static methods in java
  53. Can we Override static methods in java 
  54. Can we call super class static methods from sub class 
  55. Explain return type in java 
  56. Can we call Sub class methods using super class object? 
  57. Can we Override private methods ? 
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  59. Java programming interview questions on collections

Java Example Program to convert binary to decimal


  • Famous interview java question on conversions . 
  • We can convert binary to decimal in two ways
    1.Using Integer.parseInt() method
    2.Using custom logic



1.Write a Java Program to convert binary to decimal number in java without using Integer.parseInt() method.

  1. import java.util.Scanner;
  2. public class DecimalFromBinary {
  3.  
  4.     /**
  5.      *www.instanceofjava.com
  6.      */
  7.  
  8.  public static void main(String[] args) {
  9.         
  10.  Scanner in = new Scanner( System.in );
  11.  System.out.println("Enter a binary number: ");
  12.  
  13.   int  binarynum =in.nextInt();
  14.   int binary=binarynum;
  15.         
  16. int decimal = 0;
  17. int power = 0;
  18.  
  19. while(true){
  20.  
  21.  if(binary == 0){
  22.  
  23.         break;
  24.  
  25.  } else {
  26.  
  27.    int tmp = binary%10;
  28.    decimal += tmp*Math.pow(2, power);
  29.    binary = binary/10;
  30.    power++;
  31.  
  32.  }
  33. }
  34.         System.out.println("Binary="+binary+" Decimal="+decimal); ;
  35. }
  36.  
  37. }

Output:


  1. Enter a binary number: 
  2. 101
  3. Binary=101 Decimal=5




2.Write a Java Program to convert binary to decimal number in java using Integer.parseInt() method.



  1. import java.util.Scanner;
  2. public class ConvertBinaryToDecimal{
  3.  
  4.     /**
  5.      *www.instanceofjava.com
  6.      */
  7.  
  8.  public static void main(String[] args) {
  9.         
  10.  Scanner in = new Scanner( System.in );
  11.  
  12.  System.out.println("Enter a binary number: ");
  13.  String binaryString =input.nextLine();
  14.  
  15.  System.out.println("Result: "+Integer.parseInt(binaryString,2));

  16.  
  17. }
  18.  
  19. }


Output:


  1. Enter a binary number:
  2. 001
  3. Result: 1

java program to convert binary to decimal


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Get collection values from hashtable example

1.Basic java collection framework example program to get Value collection from hashtable

  •   Collection values()   This method used to get collection of values
  •  Important note is that if any value is removed from set the original hashtable key also removed
  1. package com.setviewHashtable;
  2.  
  3. import java.util.Hashtable;

  4. import java.util.Enumeration;
  5. import java.util.Iterator;
  6. import java.util.Set;
  7.  
  8. public class HashtableExample{
  9.  
  10. public static void main(String[] args) {
  11.   
  12.  //create Hashtable object
  13.        Hashtable<String,String> hashtable = new Hashtable<String,String>();
  14.        
  15. //add key value pairs to Hashtable
  16. hashtable.put("1","Java Interview Questions");
  17. hashtable.put("2","Java Interview Programs");
  18. hashtable.put("3","Concept and example program");
  19. hashtable.put("4","Concept and interview Questions");
  20. hashtable.put("5","Java Quiz");
  21. hashtable.put("6","Real time examples");
  22.  
  23.  
  24.  Collection c = hashtable.values();
  25.  System.out.println("Values of Collection created from Hashtable are :");
  26. //iterate through the Set of keys
  27.  
  28.  Iterator itr = c.iterator();
  29.  while(itr.hasNext())
  30.  System.out.println(itr.next());
  31.            
  32.  c.remove("Java Quiz");
  33.            
  34. System.out.println("Elements in hash table");
  35. Enumeration e=hashtable.elements();
  36.         
  37.  
  38.  while (e.hasMoreElements()) {
  39.         System.out.println(e.nextElement());
  40. }    

  41. }
  42.  
  43. }
     



Output:

  1. Values of Collection created from Hashtable are :
  2. Real time examples
  3. Java Quiz
  4. Concept and interview Questions
  5. Concept and example program
  6. Java Interview Programs
  7. Java Interview Questions
  8. Elements in hash table
  9. Real time examples
  10. Concept and interview Questions
  11. Concept and example program
  12. Java Interview Programs
  13. Java Interview Questions


Java Collections example program Get Set view of Keys from Hashtable example

1.Basic java collection framework example program to get set view from hashtable

  • Set keySet()   This method used to get set view of the keys of hashtable
  •  Important note is that if any key is removed from set the original hashtable key also removed
  1. package com.setviewHashtable;
  2.  
  3. import java.util.Hashtable;

  4. import java.util.Enumeration;
  5. import java.util.Iterator;
  6. import java.util.Set;
  7.  
  8. public class HashtableExample{
  9.  
  10. public static void main(String[] args) {
  11.   
  12.  //create Hashtable object
  13.        Hashtable<String,String> hashtable = new Hashtable<String,String>();
  14.        
  15. //add key value pairs to Hashtable
  16. hashtable.put("1","Java Interview Questions");
  17. hashtable.put("2","Java Interview Programs");
  18. hashtable.put("3","Concept and example program");
  19. hashtable.put("4","Concept and interview Questions");
  20. hashtable.put("5","Java Quiz");
  21. hashtable.put("6","Real time examples");
  22.  
  23.  
  24.  Set st = hashtable.keySet();       
  25.  System.out.println("Set created from Hashtable Keys contains :");
  26. //iterate through the Set of keys
  27.  
  28.  Iterator itr = st.iterator();
  29.  while(itr.hasNext())
  30.  System.out.println(itr.next());
  31.            
  32.  st.remove("1");
  33.            
  34. System.out.println("Elements in hash table");
  35. Enumeration e=hashtable.keys();
  36.         
  37.  
  38.  while (e.hasMoreElements()) {
  39.         System.out.println(e.nextElement());
  40. }    

  41. }
  42.  
  43. }
     



Output:

  1. Set created from Hashtable Keys contains :
  2. 6
  3. 5
  4. 4
  5. 3
  6. 2
  7. 1
  8. Elements in hash table
  9. 6
  10. 5
  11. 4
  12. 3
  13. 2

Java collections interview programming questions

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  1. Introduction to Collection Framework  

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Collection set interface: 

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Hashset Class in Collection framework: (Java programming questions)

  1. Hashset class in java  
  2.  
  3.  
  4.  

LinkedHashSet Class in Collection framework: (Java programming questions)

  1.  

Treeset Class in Collection framework: (Java programming questions)
 
  1.  
  2.  



 Collection List Interface:

  1. Collection List Interface 

ArrayList Class in Collection framework: (Java programming questions)

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  2.  
  3.  
  4.  
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Map Interface In java

  1. Map interface  

HashMap Class in Collection framework: (Java programming questions)

  1.  
  2.  
  3. Convert keys of a map to List 
  4. Convert Values of a map to List 

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  1.  
  2.  
  3.  
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  6. Comparable vs Comparator 
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Remove all elements from hashtable java example

1.Basic java example program to remove all elements from hashtable
  • Object remove(Object key)    This method used to remove value pair from hashtable
  • void clear() this method removes all elements from hashtable
  •  
  1. package com.removevalueHashtable;
  2.  
  3. import java.util.Hashtable;

  4. import java.util.Enumeration;
  5.  
  6. public class HashtableExample{
  7.  
  8. public static void main(String[] args) {
  9.   
  10.  //create Hashtable object
  11.        Hashtable<String,String> hashtable = new Hashtable<String,String>();
  12.        
  13. //add key value pairs to Hashtable
  14. hashtable.put("1","Java Interview Questions");
  15. hashtable.put("2","Java Interview Programs");
  16. hashtable.put("3","Concept and example program");
  17. hashtable.put("4","Concept and interview Questions");
  18. hashtable.put("5","Java Quiz");
  19. hashtable.put("6","Real time examples");
  20.  
  21. Object obj = ht.remove("2");
  22. System.out.println(obj + " Removed from Hashtable");
  23.  
  24. Enumeration e=hashtable.elements();
  25.           
  26.  
  27.  while (e.hasMoreElements()) {
  28.         System.out.println(e.nextElement());
  29. }    
  30. hashtable.clear();
  31.  
  32.  System.out.println("Total key value pairs in Hashtable are : " + hashtable.size());

  33. }
  34.  
  35. }
     



Output:

  1. Java Interview Programs Removed from Hashtable
  2. Real time examples
  3. Java Quiz
  4. Concept and interview Questions
  5. Concept and exampe program
  6. Java Interview Questions
  7. Total key value pairs in Hashtable are : 0

Remove key value pair from hashtable java example

1.Basic java example program to iterate keys of hashtable
  • Object remove(Object key)    This method used to remove value pair from hashtable
  1. package com.removevalueHashtable;
  2.  
  3. import java.util.Hashtable;

  4. import java.util.Enumeration;
  5.  
  6. public class HashtableExample{
  7.  
  8. public static void main(String[] args) {
  9.   
  10.  //create Hashtable object
  11.        Hashtable<String,String> hashtable = new Hashtable<String,String>();
  12.        
  13. //add key value pairs to Hashtable
  14. hashtable.put("1","Java Interview Questions");
  15. hashtable.put("2","Java Interview Programs");
  16. hashtable.put("3","Concept and example program");
  17. hashtable.put("4","Concept and interview Questions");
  18. hashtable.put("5","Java Quiz");
  19. hashtable.put("6","Real time examples");
  20.  
  21. Object obj = ht.remove("2");
  22. System.out.println(obj + " Removed from Hashtable");
  23.  
  24. Enumeration e=hashtable.elements();
  25.           
  26.  
  27.            
  28. // display search result
  29.  while (e.hasMoreElements()) {
  30.         System.out.println(e.nextElement());
  31. }    

  32. }
  33.  
  34. }
     



Output:

  1. Java Interview Programs Removed from Hashtable
  2. Real time examples
  3. Java Quiz
  4. Concept and interview Questions
  5. Concept and exampe program
  6. Java Interview Questions

Iterate through values of hashtable java

1.Basic java example program to iterate keys of hashtable
  • Enumeration elements()   This method used to get values of hashmap

  1. package com.iteartekeysHashtable;
  2.  
  3. import java.util.Hashtable;

  4. import java.util.Enumeration;
  5.  
  6. public class HashtableExample{
  7.  
  8. public static void main(String[] args) {
  9.   
  10.  //create Hashtable object
  11.        Hashtable<String,String> hashtable = new Hashtable<String,String>();
  12.        
  13. //add key value pairs to Hashtable
  14. hashtable.put("1","Java Interview Questions");
  15. hashtable.put("2","Java Interview Programs");
  16. hashtable.put("3","Concept and example program");
  17. hashtable.put("4","Concept and interview Questions");
  18. hashtable.put("5","Java Quiz");
  19. hashtable.put("6","Real time examples");
  20.  
  21.  
  22.  
  23. Enumeration e=hashtable.elements();
  24.           
  25.  
  26.            
  27. // display search result
  28.  while (e.hasMoreElements()) {
  29.         System.out.println(e.nextElement());
  30. }    

  31. }
  32.  
  33. }
     



Output:

  1. Real time examples
  2. Java Quiz
  3. Concept and interview Questions
  4. Concept and example program
  5. Java Interview Programs
  6. Java Interview Questions

Method overloading interview questions java

1.What is Method in java?

  • Method is a sub block of a class that contains logic of that class.
  • logic must be placed inside a method, not directly at class level, if we place logic at class level compiler throws an error.
  • So class level we are allowed to place variables and methods.
  • The logical statements such as method calls, calculations and printing related statements must be placed inside method, because these statements are considered as logic. 
  • For more information @ Methods in java



  1. package com.instanceofjava;
  2. class sample{
  3.  
  4. int a;
  5. int b;
  6.  
  7. System.out.println("instance of java"); // compiler throws an error.
  8.  
  9. }
  10.  

  1. package com.instanceofjava;
  2. class sample{
  3.  
  4. static int a=10;
  5.    
  6. public static void main(String args[]){

  7. System.out.println(a); // works fine,prints a value:10
  8.  
  9.  }
  10. }

2.What is meant by method overloading in java?


  • Defining multiple methods with same name is known as polymorphism.
  • Defining multiple methods with same name and with different arguments known as method overloading.

  1. package com.instanceofjava;
  2. class A{
  3.  
  4. public void show(int a){
  5. System.out.println("saidesh");
  6. }
  7.  
  8. public void show(int a,int b){
  9. System.out.println("ajay");
  10. }
  11.  
  12. public void show(float a){
  13. System.out.println("vinod");
  14. }
  15. public static void main(String args[]){
  16.  
  17. A a=new A();
  18.  
  19. a.show(10);
  20. a.show(1,2);
  21. a.show(1.2);
  22.  
  23. }
  24. }
Output:

  1. saidesh
  2. ajay
  3. vinod


3.What are the other names for method overloading?


  • Method overloading also known as static polymorphism or compile time polymorphism because at compile time itself we can tell which method going to get executed based on method arguments.
  • So method overloading also called as static binding. 

4.What are the basic rules of method overloading?

  • Defining a method with same name and differ in number of arguments
  • Defining a method with same name and differ in type of arguments
  • Defining a method with same name and differ in order of type of arguments
  • Return type of the method not involved in method overloading.

5.Can we overload static methods in java?

  • Yes. We can overload static methods in java.
  • Method overriding is not possible but method overloading is possible for static methods.
  • Before that lets see about method overloading in java.
  • lets see an example java program which explains static method overloading.
  1. class StaticMethodOverloading{
  2.  
  3. public static void staticMethod(){
  4.  
  5. System.out.println("staticMethod(): Zero arguments");
  6.  
  7.  
  8. public static void staticMethod(int a){
  9.  
  10. System.out.println("staticMethod(int a): one argument");
  11.  
  12.  
  13. public static void staticMethod(String str, int x){
  14.  
  15. System.out.println("staticMethod(String str, int x): two arguments");
  16.  
  17. }
  18.  
  19. public static void main(String []args){
  20.   
  21.   StaticMethodOverloading.staticMethod();
  22.   StaticMethodOverloading.staticMethod(12);
  23.   StaticMethodOverloading.staticMethod("Static method overloading",10);
  24.  
  25. }
  26. }


 Output:

  1. staticMethod(): Zero arguments
  2. staticMethod(int a): one argument
  3. staticMethod(String str, int x): two arguments


6.Can we overload main method in java?

Yes we can overload main method in java

Java Program to overload main method in java

  1. class mainMethodOverloading{
  2.  
  3. public static void main(boolean x){
  4.  
  5. System.out.println("main(boolean x) called ");
  6.  
  7.  
  8. public static void main(int x){
  9.  
  10. System.out.println("main(int x) called");
  11.  
  12.  
  13. public static void main(int a, int b){
  14.  
  15. System.out.println("main(int a, int b) called");
  16.  
  17. }
  18.  
  19. public static void main(String []args){
  20.    
  21.  
  22. System.out.println("main(String []args) called ");
  23.  
  24.   mainMethodOverloading.main(true);
  25.   mainMethodOverloading.main(10);
  26.  mainMethodOverloading.main(37,46);
  27.  
  28.  
  29. }
  30. }




 Output:

  1. main(String []args) called
  2. main(boolean x) called
  3. main(int x) called
  4. main(int a, int b) called

method overloading interview questions





7.Can we overload constructors in java?

  • Yes we can overload constructor in java

  1. package instanceofjava;
  2. class ConstructorChaining{
  3. int a,b 
  4. ConstructorChaining(){
  5. this(1,2);
  6.  System.out.println("Default constructor");
  7.  
  8.  
  9. ConstructorChaining(int x , int y){
  10.  
  11. this(1,2,3); 
  12. a=x;
  13. b=y;
  14.  System.out.println("Two argument constructor");
  15.  
  16. }
  17.  
  18. ConstructorChaining(int a , int b,int c){
  19.  System.out.println("Three argument constructor")
  20.  
  21. public static void main(String[] args){
  22.  
  23.  ConstructorChaining obj=new ConstructorChaining();
  24.   System.out.println(obj.a);
  25.   System.out.println(obj.b);
  26.  
  27. }
  28. }


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Iterate through keys of hashtable java

1.Basic java example program to iterate keys of hashtable
  • Enumeration keys()   This method used to get keys of hashmap

  1. package com.iteartekeysHashtable;
  2.  
  3. import java.util.Hashtable;

  4. import java.util.Enumeration;
  5.  
  6. public class HashtableExample{
  7.  
  8. public static void main(String[] args) {
  9.   
  10.  //create Hashtable object
  11.        Hashtable<String,String> hashtable = new Hashtable<String,String>();
  12.        
  13. //add key value pairs to Hashtable
  14. hashtable.put("1","Java Interview Questions");
  15. hashtable.put("2","Java Interview Programs");
  16. hashtable.put("3","Concept and exampe program");
  17. hashtable.put("4","Concept and interview Questions");
  18. hashtable.put("5","Java Quiz");
  19. hashtable.put("6","Real time examples");
  20.  
  21.  
  22.  
  23. Enumeration e=hashtable.keys();
  24.           
  25.  
  26.            
  27. // display search result
  28.  while (e.hasMoreElements()) {
  29.         System.out.println(e.nextElement());
  30. }    

  31. }
  32.  
  33. }
     



Output:

  1. 6
  2. 5
  3. 4
  4. 3
  5. 2
  6. 1

Check particular value exist in hashtable

1.Basic java example program to check particular value exist in hashtable
  • boolean contains(Object value)   This method used to check  particular value exist in hashtable

  1. package com.CheckElelemtHashtable;
  2.  
  3. import java.util.Hashtable;

  4. import java.util.Enumeration;
  5.  
  6. public class HashtableExample{
  7.  
  8. public static void main(String[] args) {
  9.   
  10.  //create Hashtable object
  11.        Hashtable<String,String> hashtable = new Hashtable<String,String>();
  12.        
  13. //add key value pairs to Hashtable
  14. hashtable.put("1","Java Interview Questions");
  15. hashtable.put("2","Java Interview Programs");
  16. hashtable.put("3","Concept and exampe program");
  17. hashtable.put("4","Concept and interview Questions");
  18. hashtable.put("5","Java Quiz");
  19. hashtable.put("6","Real time examples");
  20.  
  21.  /*
  22.  To check whether a particular value exists in Hashtable we need to use
  23.  boolean containsKey(Object value) method of Hashtable class.
  24. if the Hashtable contains mapping for specified value It returns true
  25. otherwise returns false.
  26. */
  27.        
  28.  boolean isExists = hashtable.contains("Java Quiz");
  29.  System.out.println("Java Quiz exists in Hashtable ? : " + isExists);

  30. System.out.println("Hashtable values : ");
  31.  
  32. Enumeration e=hashtable.elements();
  33.           
  34.  
  35.            
  36. // display search result
  37.  while (e.hasMoreElements()) {
  38.         System.out.println(e.nextElement());
  39. }    

  40. }
  41.  
  42. }
     



Output:

  1. Java Quiz exists in Hashtable ? : true
  2. Hashtable values : 
  3. Real time examples
  4. Java Quiz
  5. Concept and interview Questions
  6. Concept and exampe program
  7. Java Interview Programs
  8. Java Interview Questions

Check if a particular key exists in Java Hashtable example

1.Basic java example program to check particular element exist in hashtable
  • boolean containsKey(Object key)   This method used to check  particular key exist in hashtable

  1. package com.CheckElelemtHashtable;
  2.  
  3. import java.util.Hashtable;
  4. import java.util.Iterator;
  5.  
  6. public class HashtableExample{
  7.  
  8. public static void main(String[] args) {
  9.   
  10.  //create Hashtable object
  11.        Hashtable<String,String> hashtable = new Hashtable<String,String>();
  12.        
  13. //add key value pairs to Hashtable
  14. hashtable.put("1","Java Interview Questions");
  15. hashtable.put("2","Java Interview Programs");
  16. hashtable.put("3","Concept and exampe program");
  17. hashtable.put("4","Concept and interview Questions");
  18. hashtable.put("5","Java Quiz");
  19. hashtable.put("6","Real time examples");
  20.  
  21.  /*
  22.  To check whether a particular key exists in Hashtable we need to use
  23.  boolean containsKey(Object key) method of Hashtable class.
  24. if the Hashtable contains mapping for specified key It returns true
  25. otherwise returns false.
  26. */
  27.        
  28.  boolean isExists = hashtable.containsKey("5");
  29.  System.out.println("5 exists in Hashtable ? : " + isExists);

  30.  
  31.  
  32. Enumeration e=hashtable.elements();
  33.           
  34.  System.out.println("Display result:"); 
  35.            
  36. // display search result
  37.  while (e.hasMoreElements()) {
  38.         System.out.println(e.nextElement());
  39. }    

  40. }
  41.  
  42. }
     



Output:

  1. 5 exists in Hashtable ? : true
  2. Hashtable values : 
  3. Display result:
  4. Real time examples
  5. Java Quiz
  6. Concept and interview Questions
  7. Concept and exampe program
  8. Java Interview Programs
  9. Java Interview Questions

Non static blocks in java example

Non Static Blocks in java

  • When ever object created non static blocks will be executed before the execution of constructor
  • Non static blocks are class level block which does not have prototype


  1. package nonstaticblocks;
  2. public class A {
  3.  
  4.    {
  5.         
  6.        System.out.println("non static block executed");
  7.  
  8.     }
  9.  
  10. }


What is the need of Non static blocks in java?

  • To execute any logic whenever object is created irrespective of constructor used in object creation.

Who will execute Non static blocks?

  • Non static blocks are automatically called by JVM for every object creation in java stack area

How many Non static blocks we can create?
  • We can create any number of Non static blocks

Order of execution of non static blocks

  • Order of execution of non static blocks will be order as they are defined.
  1. package nonstaticblocks;
  2. public class A {
  3.  
  4. {

  5.   System.out.println("first block");
  6.  
  7. {
  8.  System.out.println("second block");
  9. }
  10.  
  11. {
  12.  System.out.println("third block");
  13. }
  14. public static void main(String[] args) {
  15.   A obj= new A();
  16. }
  17. }

 Output:

  1. first block
  2. second block
  3. third block


 Order of execution of non static blocks with respect to constructor?



non static blocks in java example program


Remove all elements LinkedHashSet example

1.Basic java example program to remove all elements in linkedhashset
  • clear()   This method used to remove all elements from Linkedhashset.

  1. package com.removeelementLinkedhashset;
  2.  
  3. import java.util.LinkedHashSet;
  4. import java.util.Iterator;
  5.  
  6. public class LinkedHashsetExample{
  7.  
  8. public static void main(String[] args) {
  9.   
  10. LinkedHashSet<String> linkedhashset = new LinkedHashSet<>();
  11.        
  12.         linkedhashset.add("Java Interview Questions");
  13.         linkedhashset.add("Java interview program");
  14.         linkedhashset.add("Concept and example program");
  15.         linkedhashset.add("Concept and interview questions");
  16.         linkedhashset.add("Java Quiz");
  17.     
  18.       
  19. System.out.println("LinkedHashSet before removal : " + linkedhashset);
  20.  
  21.   boolean blnRemoved = linkedhashset.remove("Java Quiz");
  22.   System.out.println("Was Java Quiz removed from LinkedHashSet ? " + blnRemoved);
  23.   

  24.  
  25. System.out.println("LinkedHashSet after removal : ");
  26.  
  27. Iterator it=linkedhashset.iterator();
  28.              
  29. while(it.hasNext()){
  30. System.out.println(it.next());
  31.                      
  32. }   
  33.  linkedhashset.clear();
  34.  System.out.println("LinkedHashSet after removal  all elements"); 
  35.  
  36. }
  37.  
  38. }
     



Output:

  1. LinkedHashSet before removal : [Java Interview Questions, Java interview program, Concept
  2. and example program, Concept and interview questions, Java Quiz]
  3. Was Java Quiz removed from LinkedHashSet ? true
  4. LinkedHashSet after removal :
  5. Java Interview Questions
  6. Java interview program
  7. Concept and example program
  8. Concept and interview questions
  9. LinkedHashSet after removal all elements  :[]
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