InstanceOfJava

How to Convert string to date in java

Posted by: Instanceofjava Posted date: December 26, 2014 / comment : 0 Java SE

Whenever are having a requirement of converting string (date as string ) in to date we need to use SimpledateFormat class which is present in java.text package.
To convert string to date in java we need to follow two steps.
First we need to create SimpledateFormat class object by passing pattern of date which we want as a string.
Ex: SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");
And next we need to call parse() method on the object of SimpleDateFormat then it will returns Date object.
parse() method throws ParseException so need to handle this exception.
By using format method of the object will get string format of given date
formatter.format(date).
How to convert java string to date object
Java SimpleDateFormat String to Date conversion and parsing examples

Letter	Date or Time Component	Presentation	Examples
G	Era designator	Text	AD
y	Year	Year	2015; 15
Y	Week year	Year	2009; 09
M	Month in year	Month	July; Jul;07
w	Week in year	Number	25
W	Week in month	Number	3
D	Day in year	Number	143
d	Day in month	Number	37
F	Day of week in month	Number	1
E	Day name in week	Text	Tuesday; Tue
u	Day number of week (1 = Monday, ..., 7 = Sunday)	Number	1
a	Am/pm marker	Text	PM
H	Hour in day (0-23)	Number	0
k	Hour in day (1-24)	Number	12
K	Hour in am/pm (0-11)	Number	0
h	Hour in am/pm (1-12)	Number	12
m	Minute in hour	Number	30
s	Second in minute	Number	30
S	Millisecond	Number	778
z	Time zone	General time zone	Pacific Standard Time; PST; GMT-08:00
Z	Time zone	RFC 822 time zone	-0800
X	Time zone	ISO 8601 time zone	-08; -0800; -08:00

(Ref: Oracle DOCS)

Example program on SimpleDateFormat :

1. Convert string to date in java in MMM dd, yyyy format

Input : Jan 1, 2015 (MMM dd, yyyy):

package com.instanceofjava;
public Class DateFormatDemo{
public static void main (String args[]) {
SimpleDateFormat formatter = new SimpleDateFormat("MMM dd, yyyy");
String dateInString = "Jan 1, 2015";
try{
Date date = formatter.parse(dateInString);
System.out.println(date);
System.out.println(formatter.format(date));
}catch(ParseException e){
e.printStackTrace();
}
}
}
Output:
Thu Jan 01 00:00:00 IST 2015
Jan 01, 2015

2.How to convert string into date format in java day MMM dd, yyyy format example

Input : Sat, Feb 14 2015 (E, MMM dd yyyy):

package com.instanceofjava;
public Class DateFormatDemo{
public static void main (String args[]) {
SimpleDateFormat formatter = new SimpleDateFormat("E, MMM dd yyyy");
String dateInString = "Sat, February 14 2015";
try{
Date date = formatter.parse(dateInString);
System.out.println(date);
System.out.println(formatter.format(date));
}catch(ParseException e){
e.printStackTrace();
}
}
}
Output:
Sat Feb 14 00:00:00 IST 2015
Sat, Feb 14 2015

3. Convert string to date in java in dd/MM/ yyyy format example program

Input : 01/01/2015 (dd/MM/yyyy):

package com.instanceofjava;
public Class DateFormatDemo{
public static void main (String args[]) {
SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy);
String dateInString = "01/01/2015";
try{
Date date = formatter.parse(dateInString);
System.out.println(date);
System.out.println(formatter.format(date));
}catch(ParseException e){
e.printStackTrace();
}
}
}
Output:
Thu Jan 01 00:00:00 IST 2015
01/01/2015

4. Convert string to date in java in dd-MMM-yyyy format example program

Input : 1-Jan-2015 (dd-MMM-yyyy):

package com.instanceofjava;
public Class DateFormatDemo{
public static void main (String args[]) {
SimpleDateFormat formatter = new SimpleDateFormat("dd-MMM-yyyy");
String dateInString = "1-Jan-2015";
try{
Date date = formatter.parse(dateInString);
System.out.println(date);
System.out.println(formatter.format(date));
}catch(ParseException e){
e.printStackTrace();
}
}
}
Output:
Thu Jan 01 00:00:00 IST 2015
01-Jan-2015

5. Convert string to date in java in yyyyMMdd format example program

Input : 20150101 (yyyyMMdd):

package com.instanceofjava;
public Class DateFormatDemo{
public static void main (String args[]) {
SimpleDateFormat formatter = new SimpleDateFormat("yyyyMMdd");
String dateInString = "20150101";
try{
Date date = formatter.parse(dateInString);
System.out.println(date);
System.out.println(formatter.format(date));
}catch(ParseException e){
e.printStackTrace();
}
}
}
Output:
Thu Jan 01 00:00:00 IST 2015
20150101

6.Convert string to date in java in ddMMyyyy format example program

Input : 01012015 (ddMMyyyy):

package com.instanceofjava;
public Class DateFormatDemo{
public static void main (String args[]) {
SimpleDateFormat formatter = new SimpleDateFormat("ddMMyyyy");
String dateInString = "01012015";
try{
Date date = formatter.parse(dateInString);
System.out.println(date);
System.out.println(formatter.format(date));
}catch(ParseException e){
e.printStackTrace();
}
}
}
Output:
Thu Jan 01 00:00:00 IST 2015
01012015

7.Convert string to date in java in dd-MMM-yy format example program

Input : 01-January-15 (dd-MMM-yy):

package com.instanceofjava;
public Class DateFormatDemo{
public static void main (String args[]) {
SimpleDateFormat formatter = new SimpleDateFormat("dd-MMMM-yy");
String dateInString = "01-January-2015";
try{
Date date = formatter.parse(dateInString);
System.out.println(date);
System.out.println(formatter.format(date));
}catch(ParseException e){
e.printStackTrace();
}
}
}
Output:
Thu Jan 01 00:00:00 IST 2015
01012015

8.Convert string to date in java in dd-M-yyyy HH:mm:SS format example program

JVM Architecture

Posted by: Instanceofjava Posted date: December 26, 2014 / comment : 6 Java SE

This topic clears your questions like Explain jvm architecture in java , jvm architecture in java with diagram, how JVM works internally and areas of Java Virtual Machine.

Virtual machine : In general terms Virtual machine is a software that creates an environment between the computer and end user in which end user can operate programs.
As per functionality Virtual machine is creation of number of different identical execution environments on a single computer to execute programs is called Virtual machine.
Java Virtual machine: it is also Virtual machine that runs java bytecode by creating five identical run time areas to execute class members.

Function of java virtual machine

The bytecode is generated by java compiler in a JVM understandable format.
As a programmer we develop a java application and when we compile a java program, the compiler will generate .class (dot class) file.
The .class file contains byte code (Special java instructions).
To execute a java program we take the help of JVM (java virtual machine) to the JVM we have to provide .class file as the input.

Types of JVMs:

The java 2 SDK , Standard Edition , contains two implementation of the java virtual machine

Java HotSpot Client VM
Java Hotspot Server VM

Java HotSpot Client VM:

The Hotspot Client VM is the default virtual machine of the java 2 SDK and java 2 run time environment .
As its name implies, it is tuned for best performance when running applications in a client environment by reducing application start up time and memory footprint.

Java HotSpot Server VM:

The java HotSpot server VM is designed for maximum program execution speed for applications running in a server environment.
The Java HotSpot Server VM is invoked by using the server command line option when an application , as in java server MyApp.
Some of the features java HotSpot technology , common to both VM implementations, are the following.

Adaptive compiler:

Applications are launched using a standard interpreter, but the code is then analyzed as it runes to detect performance bottlenecks, or "hot spots".
The Java HotSpot VMs compile those performance critical portions of the code for a boost in performance , while avoiding unnecessary compilation of seldom used code.
The Java HotSpot VMs also uses the adoptive compiler to decide on the fly , how best to optimize compiled code with techniques such as in lining.
The run time analysis performed by the compiler allows it to eliminate guesswork in determining which optimizations will yield the largest performance benefit.

Rapid memory allocation garbage collection:

Java HotSpot technology provides for rapid memory allocation for objects , and it has a fast, efficient, state-of-the-art garbage collector.

Thread Synchronization:

The Java programming language allows for use of multiple , concurrent paths of program execution (called threads).
Java HotSpot technology provides a thread- handling capability that is designed to scale readily for use in large , shared memory multiprocessor servers.

Jvm architecture in java with diagram

Class Loader Sub System:

The class loader sub system will take a .class file as the input and performance the following operations.
The class loader sub system is responsible for loading the .class file (Byte code) into the JVM.
Before loading the Byte code into the JVM it will verify where there the Byte code is valid or not. This verification will be done by Byte code verifier.
If the Byte code is valid then the memory for the Byte code will be allocated in different areas.
The different areas into which the Byte code is loaded are called as Run Time Data Areas. The various run time data areas are.

1.Method Area:

Java Virtual Machine Method Area can be used for storing all the class code and method code.
All classes bytecode is loaded and stored in this run time area , and all static variables are created in this area.

2.Heap Memory:

JVM Heap Area can be used for storing all the objects that are created.
It is the main memory of JVM , all objects of classes :- non static variables memory are created in this run time area.
This runtime area memory is finite memory.
This area can be configured at the time of setting up of runtime environment using non standard option like
java -xms <size> class-name.
This can be expandable by its own , depending on the object creation.
Method area and Heap area both are sharable memory areas.

3.Java Stack area:

JVM stack Area can be used for storing the information of the methods. That is under execution. The java stack can be considered as the combination of stack frames where every frame will contain the stat of a single method.
In this runtime area all Java methods are executed.
In this runtime JVM by default creates two threads. they are
1.main method
2.Garbage Collection Thread
main thread responsible to execute java methods starts with main method.
Also responsible to create objects in heap area if its finds new keyword in any method logic.
Garbage collection thread is responsible to destroy all unused objects from heap area.

4.PC Register (program counter) area:

The PC Register i Java Virtual Machine will contain address of the next instruction that have to be executed.

5.Java Native Stack:

Java native stack area is used for storing non-java coding available in the application. The non-java code is called as native code.

Execution Engine:

The Execution Engine of JVM is Responsible for executing the program and it contains two parts.

Interpreter.
JIT Compiler (just in time compiler).

The java code will be executed by both interpreter and JIT compiler simultaneously which will reduce the execution time and them by providing high performance. The code that is executed by JIT compiler is called as HOTSPOTS (company).

Java programming interview questions

Inner classes in java

Posted by: Instanceofjava Posted date: December 26, 2014 / comment : 0 Java SE

Class inside a class is known as nested class.
We will use nested classes to group classes and interfaces at one place for readability and maintainability.

package com.instanceofjava;
public class A{
class B{
// inner class
}
}

Inner class is a part of nested class. Non-static nested classes are known as inner classes.
Nested classes are two types
Non-static nested class(inner class)
1. Member inner class
2. Anonymous inner class
3. Local inner class
Static nested class.

Member inner class:

A class is defined within a class and outside of methods of that class known as member inner class.

package instanceofjavaforus;
public class A{
class B{
public void show(){
}
}
public static void main(String args[]){
A a= new A();
a.B b= a.new B();
b.show();
}
}

Anonymous inner class:

Anonymous inner class is a inner class which does not have a name and whose instance is created at the time creating class itself.
Anonymous inner classes are somewhat different from normal classes in its creation.
There are two ways to create in two ways.
1. Using class.
2. Using interface.

Using class:

package instanceofjavaforus;
public class A{
public void show(){
}
public static void main(String args[]){
A a= new A(){
public void display(){
System.out.println('anonymous class method');
}
};
a.display();
}
}

Using interface:

package instanceofjavaforus;
public interface A{
public void show();
}

package instanceofjavaforus;
public class Demo{
public static void main(String args[]){
A a= new A(){
public void show(){
System.out.println('anonymous class method');
}
};
a.show();
}
}

Local inner class:

A class which is defined inside a method of another class known as local inner class

package instanceofjavaforus;
public class Demo{
void create(){
class A{
void show(){
System.out.println("local inner class method");
}
}
A a= new A();
a.show();
}
public static void main(String args[]){
Demo obj= new Demo();
obj.create();
}
}

Static nested class:

A static nested class is a class which is defined inside a class as static.

package instanceofjavaforus;
public class Outer{
static class inner{
public void show(){
System.out.println("static inner class method");
}
}
public static void main(String args[]){
Outer.inner in= new Outer.innner();
in.show();
}
}

Access Specifiers/modifiers in java

Posted by: Instanceofjava Posted date: December 25, 2014 / comment : 1 Java SE

Access Specifier:

To Explicitly mention the way how the data (variables and methods of a class) available to outside.
Access specifier is something which mentions the way how the member of a class has to be available to anything outside the class.
Access specifiers not not applicable to the local variables.(present inside method).
Access specifiers are the keywords using which we can control the accessibility of the members of a class.
There are 4 different ways in which we can control the accessibility of the members of a class
Thus there are "4" access specifiers and they are,

public
private
protected
default (not a keyword)

if we not specify any keyword that will be considered as default

Public:

The access specifier "public" makes the member of a class available to any location outside of the class.
Thus anything mentioned as public would be available to any location outside the class.
Means if we have a class with public access specifier then we can use it in other packages also by importing the corresponding package.

package package1;
public Class A{
public void show(){
}
public static void main (String args[]) {
}
}

package package2;
import package1.*;
public Class B {
public static void main (String args[]) {
A a = new A();
a.show();
}
}

Private:

Private would not allow the member of class available to any location outside the class.
private members would be available only within the same class.
Private members of a class would not be available to anything outside the class under any condition.
Private members of a class would also be not available to the sub class objects

package package1;
Class A{
private void show(){
}
public static void main (String args[]) {
A a= new A();
a.show();
}
}

Default:

Any member of class mentioned without any access specifier then its considers that as default .
Default will act as "public " within the same package and same path.
The same default would act as private outside the package.
Default members of any class would be available to anything within the same package and would not be available outside the package under any condition.

package package1;
Class A{
void show(){
}
public static void main (String args[]) {
A a= new A(); // works fine in same class
a.show();
}
}

package package1;
Class B{
public static void main (String args[]) {
A a= new A(); // works fine in same package
a.show();
}
}

package package2;
import package1.*;
Class B{
public static void main (String args[]) {
A a= new A(); // gives an error
a.show(); // gives an error
}
}

Protected:

protected will act as public within the same package and acts as private outside the package.
But protected will also act as public outside the package only with respect to sub class objects.

package package1;
public Class A{
protected void show() {
}
}

package package2;
import package1.*;
public Class B extends A {
public static void main (String args[]) {
B b= new B();
b.show();
}
}

Access specifiers are applicable to static inner class and member inner class.
Access specifiers are not applicable to anonymous inner class and local inner class

Packages in java

Posted by: Instanceofjava Posted date: December 25, 2014 / comment : 0 Java SE

Package:

Packages are nothing but all the related classes and interfaces and .class files.
Packages are the folders which are binding all the related ".class " files together
Binding: making something available to related functionalities.
A simple folder would only groups all the related files . But where as packages are also folders which binds all the related files.
Every package would be a folder. But every folder can not be a package

How to create user defined package:

By using a keyword "package".
package package_name.

package instanceofjavaforus;
Class Demo{
public static void main (String args[]) {
}
}

The Directory Structure of Packages:

To make java compiler to crate a package for us and automatically load all corresponding files into package

package instanceofjavaforus;
public Class Demo{
public static void main (String args[]) {
}
}

Save this as Demo.java
At this time there is no folder with name instanceofjavaforus
Javac -d . Demo.java.
-d : creates directory
instanceofjavaforus -> Demo.java: a folder with name instanceofjavaforus will be created and inside Demo.class will be there.

Creating Sub packages:

Create a package with a class;

package pack;
public Class Demo{
public static void main (String args[]) {
}
}

C:/> javac -d . Demo.java
Now pack-> Demo.class folder structure will be created.
Now create sub package like this.

package pack.subpack;
public Class Abc{
public static void main (String args[]) {
}
}

c:/> javac -d . Abc.java
pack->subpack -> Demo.class,Abc.class

How to create jar file representing our package:

By using dos command
c:/> jar -cvf file_name package_name.
Ex: jar -cvf instanceofjava.jar pack

Importing a package:

We can import packages by using "import".
To import the package
import<space><package-name><.><* or name of class you want to use from that package
To import particular class inside a package>.
import<space><package-name><.><name of class you want to use from that package>
As per the naming convention: For package names use small case letters.

import pack.Demo;
public Class Xyz extends Demo {
public static void main (String args[]) {
}
}

import pack.*;
public Class Xyz extends Demo {
public static void main (String args[]) {
}
}

Commonly using Predefined packages in java:

Java.lang:

Provides classes that are fundamental to the design of the Java programming language. like

Integer
boolean
Class
Object
Runtime
Thread
System
Process
Package
String

Java.util.*:

This package contains the collections framework classes, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous. some of the interfaces and classes present in java.util package are as follows.

Collection
Comparator
Enumeration
RandomAccess
List
Set
Map
Iteraot
EventListener
Scanner (class)

Java.io.* :

This package provides classes and interfaces for system input and output through data streams, serialization and the file system.Some of the classes present in java.io package are as follows.

BufferedInputStream
BufferedOutputStream
BufferedReader
SerializablePermission
Console
File
FileReader
FilerWriter
InputStream
PrintStream

Java.text.* :

This package is used for formatting date and time on day to day business
operations.Some of the classes present in java.text package are as follows

Annotation
Collater
Format
DateFormat
DecimalFormat
MessageFormat
NumberFormat
Normalizer
RuleBasedCollator
ParsePosition

Java.sql.*

This package is used for retrieving the data from data base and performing
various operations on data base. here some of the classes present in java.sql.

Drivermanger
Date
Time
SqlPermission
Timestamp

some of the interfaces present in java.sql package

CallableStatement
Connection
PreparedStatement
ResultSet
Statement
SQLData
SQLInput
SQLOutput

What is the difference between equals() method and == operator

Posted by: Instanceofjava Posted date: December 24, 2014 / comment : 0 Core java Interview Questions

== operator:

== operator used to compare objects references.
used to compare data of primitive data types
if we are comparing two objects using "==" operator if reference of both are same then it will returns true otherwise returns false.
obj1==obj2;
If we are comparing primitive data type variables then it compares data of those two variables
Ex: int a=12; int b=12; if(a==b) returns true

Comparing primitive values:

package com.instanceofjava;
Class Demo{
public static void main (String args[]) {
int a=12;
int b=13;
int c=12;
if(a==b){
System.out.println("a and b are equal");
}
if(b==c){
System.out.println("a and b are equal");
}
}
}

Comparing Objects:

package com.instanceofjavaforus;
Class Demo{
public static void main (String args[]) {
Demo obj1= new Demo();
Demo obj2=new Demo();
if(obj1==obj2){ // here both are two different objects(memory allocation wise);
System.out.println("obj1 and obj2 are referring to same address");
}else{
System.out.println("obj1 and obj2 are referring to different address");
}
}
}

Comparing String Objects:

package com.instanceofjava;
Class ComapreStringDemo{
public static void main (String args[]) {
String s1=new String("abc");
String s2=new String("abc");
if(s1==s2){ // here it returns false
System.out.println("obj1 and obj2 are referring to same address");
}else{
System.out.println("obj1 and obj2 are referring to different address");
}
}
}

Comparing String Literals:

If we declared two string literals with same data then those will refer same reference.
means if we create any object using string literal then it will be created in string pool
then if we are created another literal with same data then it wont create another object rather refers same object in pool.
so if compare two string literals with same data using "==" operator then it returns true.

package com.instanceofjava;
Class ComapreStringLiteralDemo{
public static void main (String args[]) {
String s1="abc";
String s2="abc";
if(s1==s2){ // here it returns true
System.out.println("obj1 and obj2 are referring to same address");
}else{
System.out.println("obj1 and obj2 are referring to different address");
}
}
}

equals() method:

equals() method defined in "object" class.
By default equals methods behaves like "==" operator when comparing objects.
By default equals() method compares references of objects.
But All wrapper classes and String class overriding this equals method and comparing data .
Means in String class and in All wrapper classes this equals() methods is overridden so that to compare data of those class objects.

Comparing String Objects:

package com.instanceofjava;
Class ComapreStringDemo{
public static void main (String args[]) {
String s1=new String("abc");
String s2=new String("abc");
if(s1.equals(s2)){ // here it returns true
System.out.println(" data present in obj1 and obj2 is same");
}else{
System.out.println(" data present in obj1 and obj2 is different");
}
}
}

Comparing custom objects:

If we want to compare custom objects means our own objects data.
Then we need to override equals method and in that we need to compare data.

package com.instanceofjavaforus;

public class Patient {
   String name;
   Patient(String name){
       this.name=name;
   }
      public boolean equals(Patient obj){

       if(this.name.equals(obj)){
           return true;
       }else{
           return false;
       }
   }
       public static void main(){
        Patient obj1= new Patient("sam");

        Patient obj2= new Patient("sam");

        System.out.println(obj1.equals(obj2)); //returns true
    }

}

Important points to note about equals() and "==":

"==" used to compare data for primitive data type variables .
"==" operator compares objects references
By default equals() method behaves like "==" operator for objects means compares objects references.
All wrapper classes and String class overriding this equals() method and compares data of two objects. if same returns true.(when ever we overrides equals() method we need to override hashcode() method too and if two objects on equal method same then both should have same hashcode).
And in equals() method in string class logic includes "==" operator too.

package com.instanceofjava;
public boolean equals(Object anObject) {
if (this == anObject) {
return true;
}
if (anObject instanceof String) {
String anotherString = (String) anObject;
int n = value.length;
if (n == anotherString.value.length) {
char v1[] = value;
char v2[] = anotherString.value;
int i = 0;
while (n-- != 0) {
if (v1[i] != v2[i])
return false;
i++;
}
return true;
}
}
return false;
}

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How to Convert string to date in java

Example program on SimpleDateFormat :

1. Convert string to date in java in MMM dd, yyyy format

Input : Jan 1, 2015 (MMM dd, yyyy):

2.How to convert string into date format in java day MMM dd, yyyy format example

Input : Sat, Feb 14 2015 (E, MMM dd yyyy):

3. Convert string to date in java in dd/MM/ yyyy format example program

Input : 01/01/2015 (dd/MM/yyyy):

4. Convert string to date in java in dd-MMM-yyyy format example program

Input : 1-Jan-2015 (dd-MMM-yyyy):

5. Convert string to date in java in yyyyMMdd format example program

Input : 20150101 (yyyyMMdd):

6.Convert string to date in java in ddMMyyyy format example program

Input : 01012015 (ddMMyyyy):

7.Convert string to date in java in dd-MMM-yy format example program

Input : 01-January-15 (dd-MMM-yy):

8.Convert string to date in java in dd-M-yyyy HH:mm:SS format example program

JVM Architecture

Function of java virtual machine

Types of JVMs:

Java HotSpot Client VM:

Java HotSpot Server VM:

Adaptive compiler:

Rapid memory allocation garbage collection:

Thread Synchronization:

Jvm architecture in java with diagram

Class Loader Sub System:

1.Method Area:

2.Heap Memory:

3.Java Stack area:

4.PC Register (program counter) area:

5.Java Native Stack:

Execution Engine:

Inner classes in java

Member inner class:

Anonymous inner class:

Using class:

Using interface:

Local inner class:

Static nested class:

Top 25 Core java interview questions for freshers

1. what is a transient variable?

2. What is synchronization?

3. What’s new with the stop(), suspend() and resume() methods in JDK 1.2?

4. Is null a keyword?

5. What state does a thread enter when it terminates its processing?

6. What is the Collections API?

7. What is the List interface?

8. What is the Vector class?

9.Can we instantiate Abstract class?

10.What is the first keyword used in a java program?

11.When a class should be defined as final?

12.Can we declare abstract method as static?

13.Can we apply abstract keyword to interface?

14.Can we write empty interface?

15.Can we declare interface as final?

16.How to solve ClassCastException?

17. Is “xyz” a primitive value?

18.When is an object subject to garbage collection?

19.What method must be implemented by all threads?

20.What happens if an exception is not caught?

21.How are this() and super() used with constructors?

22.Under what conditions is an object’s finalize() method invoked by the garbage collector?

23.What restrictions are placed on method overloading?

24.When does the compiler supply a default constructor for a class?

25.What modifiers can be used with a local inner class?