Six different ways to iterate list in java

Posted by: Instanceofjava Posted date: March 11, 2016 / comment : 1

How many ways we can iterate list in java?

  • We can iterate list in 6  different ways in java.
  1. For Loop
  2. Enhanced For Loop
  3. While Loop
  4. Iterator
  5. Collections stream() util (Java8 feature)
  6. ListIterator

different ways to iterate list in java


1. Iterate list using For loop


1.Basic Java example program to iterate arraylist elements using list iterator
  1. package com.javaIteratelist;
  2.  
  3. import java.util.ArrayList;
  4. import java.util.Collections;
  5. import java.util.Iterator;
  6.  
  7. public class IterateList{
  8.  
  9. public static void main(String[] args) {
  10.   
  11. //create an ArrayList object
  12.  List<String> instanceofjavaList = new ArrayList<String>();
  13.        
  14. //Add elements to Arraylist
  15.  
  16. // add 5 different values to arraylist 
  17. instanceofjavaList.add("Interview Questions");
  18. instanceofjavaList.add("Interview Programs");
  19. instanceofjavaList.add("Concept and example program");
  20. instanceofjavaList.add("Concept and interview questions");
  21. instanceofjavaList.add("Java Quiz");
  22.     
  23. for (int i = 0; i < instanceofjavaList.size(); i++) {
  24.  
  25.     System.out.println(instanceofjavaList.get(i));
  26.  
  27. }

  29. }
  30.  
  31. }
     



Output:

  1. Interview Questions
  2. Interview Programs
  3. Concept and example program
  4. Concept and interview questions
  5. Java Quiz


 2. Iterate list using Enhanced For loop

  1. package com.javaIteratelist;
  2.  
  3. import java.util.ArrayList;
  4. import java.util.Iterator;
  5.  
  6. public class IterateList{
  7.  
  8. public static void main(String[] args) {
  9.   
  10. //create an ArrayList object
  11. List<String> instanceofjavaList = new ArrayList<String>();
  12.        
  13. //Add elements to Arraylist
  14.  
  15. // add 5 different values to arraylist 
  16. instanceofjavaList.add("Interview Questions");
  17. instanceofjavaList.add("Interview Programs");
  18. instanceofjavaList.add("Concept and example program");
  19. instanceofjavaList.add("Concept and interview questions");
  20. instanceofjavaList.add("Java Quiz");
  21.  
  22. for (String str: instanceofjavaList) {
  23.             System.out.println(str);
  24. }

  26. }
  27.  
  28. }
     


Output:

  1. Interview Questions
  2. Interview Programs
  3. Concept and example program
  4. Concept and interview questions
  5. Java Quiz


 3. Iterate list using while loop

  1. package com.javaIteratelist;
  2.  
  3. import java.util.ArrayList;
  4. import java.util.Iterator;
  5.  
  6. public class IterateList{
  7.  
  8. public static void main(String[] args) {
  9.   
  10. //create an ArrayList object
  11. List<String> instanceofjavaList = new ArrayList<String>();
  12.        
  13. //Add elements to Arraylist
  14.  
  15. // add 5 different values to arraylist 
  16. instanceofjavaList.add("Interview Questions");
  17. instanceofjavaList.add("Interview Programs");
  18. instanceofjavaList.add("Concept and example program");
  19. instanceofjavaList.add("Concept and interview questions");
  20. instanceofjavaList.add("Java Quiz");
  21.  
  22.  
  23. int i = 0;
  24.  
  25. while (i < instanceofjavaList.size()) {
  26.  
  27.   System.out.println(instanceofjavaList.get(i));
  28.   i++;
  29. }

  31. }
  32.  
  33. }
     


Output:

  1. Interview Questions
  2. Interview Programs
  3. Concept and example program
  4. Concept and interview questions
  5. Java Quiz

 4. Iterate list using iterator

  1. package com.javaIteratelist;
  2.  
  3. import java.util.ArrayList;
  4. import java.util.Iterator;
  5.  
  6. public class IterateList{
  7.  
  8. public static void main(String[] args) {
  9.   
  10. //create an ArrayList object
  11. List<String> instanceofjavaList = new ArrayList<String>();
  12.        
  13. //Add elements to Arraylist
  14.  
  15. // add 5 different values to arraylist 
  16. instanceofjavaList.add("Interview Questions");
  17. instanceofjavaList.add("Interview Programs");
  18. instanceofjavaList.add("Concept and example program");
  19. instanceofjavaList.add("Concept and interview questions");
  20. instanceofjavaList.add("Java Quiz");
  21.  
  22.  
  23. Iterator<String> itr = instanceofjavaList.iterator();
  24.  
  25. while (itr.hasNext()) {
  26.      System.out.println(itr.next());
  27. }
  28.  
  29. }
  30.  
  31. }
     


Output:

  1. Interview Questions
  2. Interview Programs
  3. Concept and example program
  4. Concept and interview questions
  5. Java Quiz


 5. Iterate list using Stream API.

  1. package com.javaIteratelist;
  2.  
  3. import java.util.ArrayList;
  4. public class IterateList{
  5.  
  6. public static void main(String[] args) {
  7.   
  8. //create an ArrayList object
  9. List<String> instanceofjavaList = new ArrayList<String>();
  10.        
  11. //Add elements to Arraylist
  12.  
  13. // add 5 different values to arraylist 
  14. instanceofjavaList.add("Interview Questions");
  15. instanceofjavaList.add("Interview Programs");
  16. instanceofjavaList.add("Concept and example program");
  17. instanceofjavaList.add("Concept and interview questions");
  18. instanceofjavaList.add("Java Quiz");
  19.  
  20.  
  21. instanceofjavaList.forEach((name) -> {
  22.             System.out.println(name);
  23.         }); 

  25. }
  26.  
  27. }
     


Output:

  1. Interview Questions
  2. Interview Programs
  3. Concept and example program
  4. Concept and interview questions
  5. Java Quiz

6. Using List erator:

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1.What are all the different places to create object in java

Java program to insert an element to ArrayList using ListIterator Example

Posted by: Instanceofjava Posted date: March 11, 2016 / comment : 1 , ,

1.Basic Java example program to insert element using list iterator to arraylist
  1. package com.javaIteratearraylistiterator;
  2.  
  3. import java.util.ArrayList;
  4. import java.util.Collections;
  5. import java.util.Iterator;
  6.  
  7. public class IterateListIteratorArrayList{
  8.  
  9. public static void main(String[] args) {
  10.   
  11. //create an ArrayList object
  12. ArrayList<String> arrayList = new ArrayList();
  13.        
  14. //Add elements to Arraylist
  15.  
  16. arrayList.add("A");
  17. arrayList.add("B");
  18. arrayList.add("C");
  19. arrayList.add("D");
  20. arrayList.add("F");
  21. arrayList.add("F");
  22. arrayList.add("G");
  23. arrayList.add("H");
  24. arrayList.add("I");
  25.     
  26.         
  27.  /*
  28. Get a ListIterator object for ArrayList using
  29. istIterator() method.
  30. */
  31.   
  32. System.out.println("Before inserting element");
  33.  
  34. for(int intIndex = 0; intIndex < arrayList.size(); intIndex++)
  35.               System.out.println(arrayList.get(intIndex)); 
  36. ListIterator itr = arrayList.listIterator();
  37.        
  38. /*
  39.       Use void add(Object o) method of ListIterator to add or insert an element
  40.       to List. It adds an element just before the element that would have
  41.       been returned by next method call and after the element that would have
  42.       returned by previous call.
  43.     */
  44.    
  45.     itr .next();
  46.        
  47.     //Add an element
  48.     itr .add("Added Element");
  49.     /*
  50.  
  51. System.out.println("After inserting element .");
  52.  
  53. for(int intIndex = 0; intIndex < arrayList.size(); intIndex++)
  54.               System.out.println(arrayList.get(intIndex));   
  55.  
  56. }
  57. }
     



Output:

  1. Before inserting element
  2. A
  3. B
  4. C
  5. D
  6. F
  7. F
  8. G
  9. H
  10. I
  11. After inserting element .
  12. A
  13. Added Element
  14. B
  15. C
  16. D
  17. F
  18. F
  19. G
  20. H
  21. I

How to sort arraylist of strings alphabetically java

Posted by: Instanceofjava Posted date: March 10, 2016 / comment : 0 ,

1.Basic Java example program to sort arraylist of strings

  1. package com.javasortarraylistofobjects;
  2.  
  3. import java.util.ArrayList;
  4. import java.util.Collections;
  5. import java.util.Iterator;
  6.  
  7. public class SortArrayList{
  8.  
  9. public static void main(String[] args) {
  10.   
  11. //create an ArrayList object
  12. ArrayList<String> arrayList = new ArrayList();
  13.        
  14. //Add elements to Arraylist
  15.         
  16. arrayList.add("A"); 
  17. arrayList.add("C");
  18. arrayList.add("D");
  19. arrayList.add("Z");
  20. arrayList.add("F");
  21. arrayList.add("J");
  22. arrayList.add("K");
  23. arrayList.add("M");
  24. arrayList.add("L");
  25. arrayList.add("O");
  26.        
  27.         
  28.  System.out.println("Before sorting ArrayList ...");
  29.  Iterator itr=arrayList.iterator();
  30.         
  31. while (itr.hasNext()) {
  32.  
  33. System.out.println(itr.next());
  34.      
  35. }
  36.  
  37.        
  38.  /*
  39.  To sort an ArrayList object, use Collection.sort method. This is a
  40.   static method. It sorts an ArrayList object's elements into ascending order.
  41. */
  42.   Collections.sort(arrayList);
  43.      
  44.   System.out.println("After sorting ArrayList ...");
  45.        
  46.     
  47.         
  48. Iterator itr1=arrayList.iterator();
  49.         
  50. while (itr1.hasNext()) {

  52. System.out.println(itr1.next());
  53.             
  54. }
  55.     
  56.   
  57. }
  58. }
     




Output:

  1. Before sorting ArrayList ...
  2. A
  3. C
  4. D
  5. Z
  6. F
  7. J
  8. K
  9. M
  10. L
  11. O
  12. After sorting ArrayList ...
  13. A
  14. C
  15. D
  16. F
  17. J
  18. K
  19. L
  20. M
  21. O
  22. Z

Java Program to Sort elements of Java ArrayList Example

Posted by: Instanceofjava Posted date: March 10, 2016 / comment : 0 ,

1.Basic Java example program to sort arraylist of integers

  1. package com.javasortarraylistofobjects;
  2.  
  3. import java.util.ArrayList;
  4. import java.util.Collections;
  5. import java.util.Iterator;
  6.  
  7. public class SortArrayList{
  8.  
  9. public static void main(String[] args) {
  10.   
  11. //create an ArrayList object
  12.  ArrayList<Integer> arrayList = new ArrayList<Integer>();
  13.        
  14.  //Add elements to Arraylist
  15. arrayList.add(10);
  16. arrayList.add(7);
  17. arrayList.add(11);
  18. arrayList.add(4);
  19. arrayList.add(9);
  20. arrayList.add(6);
  21. arrayList.add(2);
  22. arrayList.add(8);
  23. arrayList.add(5);
  24. arrayList.add(1);
  25.         
  26.         
  27.  System.out.println("Before sorting ArrayList ...");
  28.  Iterator itr=arrayList.iterator();
  29.         
  30. while (itr.hasNext()) {
  31.  
  32. System.out.println(itr.next());
  33.      
  34. }
  35.  
  36.        
  37.  /*
  38.  To sort an ArrayList object, use Collection.sort method. This is a
  39.   static method. It sorts an ArrayList object's elements into ascending order.
  40. */
  41.   Collections.sort(arrayList);
  42.      
  43.   System.out.println("After sorting ArrayList ...");
  44.        
  45.     
  46.         
  47. Iterator itr1=arrayList.iterator();
  48.         
  49. while (itr1.hasNext()) {

  51. System.out.println(itr1.next());
  52.             
  53. }
  54.     
  55.   
  56. }
  57. }
     



Output:

  1. Before sorting ArrayList ...
  2. 10
  3. 7
  4. 11
  5. 4
  6. 9
  7. 6
  8. 2
  9. 8
  10. 5
  11. 1
  12. After sorting ArrayList ...
  13. 1
  14. 2
  15. 4
  16. 5
  17. 6
  18. 7
  19. 8
  20. 9
  21. 10
  22. 11

Basic Java example program to replace an element at specified index arraylist

Posted by: Instanceofjava Posted date: March 10, 2016 / comment : 0 ,

1.Basic java Example program to replace an element at specified index java arrayList.

  1. package com.instanceofjavaforus;
  2. import java.util.ArrayList;
  3.  
  4. public class ReplaceArrayList{
  5.  
  6. public static void main(String[] args) {
  7.   
  8. //create an ArrayList object
  9.  ArrayList<Integer> arrayList = new ArrayList<Integer>();
  10.        
  11.         //Add elements to Arraylist
  12.         arrayList.add(1);
  13.         arrayList.add(2);
  14.         arrayList.add(3);
  15.         arrayList.add(4);
  16.         arrayList.add(5);
  17.         arrayList.add(6);
  18.         arrayList.add(7);
  19.         arrayList.add(8);
  20.         arrayList.add(9);
  21.         arrayList.add(10);
  22.         
  23.  
  24.   /*
  25.   To replace an element at the specified index of ArrayList use
  26.   Object set(int index, Object obj) method.
  27.   This Object set(int index, Object obj) method replaces the specified element at the specified
  28.   index in the ArrayList and returns the element previously at the specified position.
  29.   */
  30.  
  31.  arrayList.set(1,23);
  32.      
  33.  System.out.println("ArrayList contains...");
  34.  Iterator itr=arrayList.iterator();
  35.  
  36. while (itr.hasNext()) {
  37.  
  38.  System.out.println(itr.next());
  39.  
  40.  }
  41.   
  42. }
  43. }
     



Output:

  1. ArrayList contains...
  2. 1
  3. 23
  4. 3
  5. 4
  6. 5
  7. 6
  8. 7
  9. 8
  10. 9
  11. 10

Java Coding Interview programming Questions : Java Test on HashMap

Posted by: Instanceofjava Posted date: February 15, 2016 / comment : 0

1.What will be the Output of this program.


  1. public class HashMapJavaTricky{
  2.  
  3. public static void main(String[] args) {
  4.  
  5.     HashMap<Integer,String> hm= new HashMap<Integer, String>();  

  7.      hm.put(1, "one");
  8.      hm.put(2, "two");
  9.      hm.put(3, "three");
  10.  
  11.     System.out.println(hm.size()); 
  12.  
  13. for (Integer name: hm.keySet()){
  14.  
  15.    System.out.println(name + " " + hm.get(name)); 
  16.   
  17. }
  18.  
  19. }
  20. }





2.Basics of java programming : Hashmap

  1. public class HashMapJavaTricky{
  2.  
  3. public static void main(String[] args) {
  4.  
  5.     HashMap<Integer,String> hm= new HashMap<Integer, String>();  

  7.      hm.put(1, "one");
  8.      hm.put(2, "two");
  9.      hm.put(3, "three");
  10.  
  11.      hm.put(1, "ONE");
  12.  
  13.     System.out.println(hm.size()); 
  14.  
  15. for (Integer name: hm.keySet()){
  16.  
  17.    System.out.println(name + " " + hm.get(name)); 
  18.   
  19. }
  20.  
  21. }
  22. }









3.Java programming examples: Hashmap

  1. public class HashMapJavaTricky{
  2.  
  3. public static void main(String[] args) {
  4.  
  5.     HashMap<Integer,String> hm= new HashMap<Integer, String>();  

  7.      hm.put(1, "one");
  8.      hm.put(2, "two");
  9.      hm.put(3, "three");
  10.  
  11.      hm.put(1, "ONE");
  12.      hm.put(null,null);
  13.  
  14.     System.out.println(hm.size()); 
  15.  
  16. for (Integer name: hm.keySet()){
  17.  
  18.    System.out.println(name + " " + hm.get(name)); 
  19.   
  20. }
  21.  
  22. }
  23. }






4.Java programming for beginners : HashMap

  1. public class HashMapJavaTricky{
  2.  
  3. public static void main(String[] args) {
  4.  
  5.     HashMap<Integer,String> hm= new HashMap<Integer, String>();  

  7.      hm.put(1, "one");
  8.      hm.put(2, "two");
  9.      hm.put(3, "three");
  10.  
  11.      hm.put(1, "ONE");
  12.      hm.put(null,null);
  13.  
  14.      Integer i=null;
  15.      String str="java programming basics Interview questions";
  16.  
  17.      hm.put(i, str);
  18.  
  19.     System.out.println(hm.size()); 
  20.  
  21. for (Integer name: hm.keySet()){
  22.  
  23.    System.out.println(name + " " + hm.get(name)); 
  24.   
  25. }
  26.  
  27. }
  28. }





Top 20 collection framework interview questions and answers in java

Posted by: Instanceofjava Posted date: July 21, 2015 / comment : 3 ,

Java collections interview questions:
collections interview questions

1.Why Map interface doesn’t extend Collection interface?

  • Set is unordered collection and does not allows duplicate elements.
  • List is ordered collection allows duplicate elements.
  • Where as Map is key-value pair.
  • It is viewed as set of keys and collection of values.
  • Map is a collection of key value pairs so by design they separated from collection interface.


2.What is difference between HashMap and Hashtable?

  • Synchronization or Thread Safe 
  • Null keys and null values 
  • Iterating the values 
  •  Default Capacity 
hashmap vs hashtable

    Click here for the
    Differences between HashMap and Hash-table

    3.Differences between comparable and comparator?

    • Comparable Interface is actually from java.lang package.
    • It will have a method compareTo(Object obj)to sort objects
    • Comparator Interface is actually from java.util package.
    • It will have a method compare(Object obj1, Object obj2)to sort objects
    Read more :  comparable vs comparator

    4.How can we sort a list of Objects?

    •  To sort the array of objects we will use  Arrays.sort() method.
    • If we need to sort collection of object we will use Collections.sort().

    5.What is difference between fail-fast and fail-safe?

    • Fail fast is nothing but immediately report any failure. whenever a problem occurs fail fast system fails. 
    • in java Fail fast iterator while iterating through collection of objects sometimes concurrent modification exception will come there are two reasons for this.
    • If one thread is iterating a collection and another thread trying to modify the collection.
    • And after remove() method call if we try to modify collection object



    6. What is difference between Iterator ,ListIterator and Enumeration?

    • Enumeration interface implemented in java 1.2 version.So Enumeration is legacy interface.
    • Enumeration uses elements() method.
    • Iterator is implemented on all Java collection classes.
    • Iterator uses iterator() method.
    • Iterator can traverse in forward direction only.
    • ListIterator is implemented only for List type classes
    • ListIterator uses listIterator() method.
    Read more :  

    What is difference between Iterator ,ListIterator and Enumeration?

    7.What is difference between Set and List in Java?

    • A set is a collection that allows unique elements.
    • Set does not allow duplicate elements
    • Set allows only one null value.
    • Set having classes like :
    • HashSet
    • LinkedHashSet
    • TreeSet
    • List having index. and ordered  collection
    • List allows n number of null values.
    • List will display Insertion order with index.
    • List having classes like :
    • Vector
    • ArrayList
    • LinkedList

    8.Differences between arraylist and vector?

    • Vector was introduced in  first version of java . that's the reason only vector is legacy class.
    • ArrayList was introduced in java version1.2, as part of java collections framework.
    • Vector is  synchronized. 
    • ArrayList is not synchronized.

    9.What are the classes implementing List interface?

    • ArrayList     
    • LinkedList     
    • Vector

    10. Which all classes implement Set interface ?

    • HashSet
    • LinkedHashSet
    • TreeSet

    11.How to make a collection thread safe?

    • Vector, Hashtable, Properties and Stack are synchronized classes, so they are thread-safe and can be used in multi-threaded environment.
    • By using Collections.synchronizedList(list)) we can make list classes thread safe.
    • By using 
      java.util.Collections.synchronizedSet()  we can make set classes thread safe.

    12.Can a null element added to a TreeSet or HashSet?

    • One null element can be added to hashset.
    • TreeSet does not allow null values

    13. Explain Collection’s interface hierarchy?


    Collections interview Questions and answers java

    14.Which design pattern Iterator follows?

    • Iterator design pattern

    15.Which data structure HashSet implements

    • Hashset implements hashmap internally.

    16.Why doesn't Collection extend Cloneable and Serializable?

    • List and Set and queue extends Collection interface.
    • SortedMap extends Map interface.

    17.What is the importance of hashCode() and equals() methods? How they are used in Java?

    • equals() and hashcode() methods defined in "object" class. 
    • If equals() method return true on comparing two objects then hashcode() of those two objects must be same.

    18.What is difference between array & arraylist?

    • Array is collection of similar type of objects and fixed in size.
    • Arraylist is collection of homogeneous and heterogeneous elements.

    19.What is the Properties class?

    • Properties is a subclass of Hashtable. It is used to maintain lists of values in which the key and the value is String.

    20.How to convert a string array to arraylist?

    • ArrayList al=new ArrayList( Arrays.asList( new String[]{"java", "collection"} ) ); 
    •  arrayList.toArray(); from list to array


    22.Java Collection framework programming interview questions 



    1. Print prime numbers? 
    2. Java Program Find Second highest number in an integer array 
    3. Java Interview Program to find smallest and second smallest number in an array 
    4. Java Coding Interview programming Questions : Java Test on HashMap  
    6. Constructor chaining in java with example programs 
    8. Swap two numbers without using third variable in java 
    9. Find sum of digits in java 
    10. How to create immutable class in java 
    11. AtomicInteger in java 
    12. Check Even or Odd without using modulus and division  
    13. String Reverse Without using String API 
    14. Find Biggest substring in between specified character
    15. Check string is palindrome or not?
    16. Reverse a number in java? 
    17. Collections interview questions and programs
     For more interview programs: Top 40 java interview programs


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