Java Tutorial

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Java Loops

Java Do While Loop Java While Loop Java For Loop Java Enhanced For Loop

Java Programs

Java Basic Programs Factorial Program in Java Fibonacci Series Program in Java Prime Number Program in Java Palindrome Number Program in Java Armstrong Number Program in Java Anagram Program in Java Pattern Programs in Java Calculator Program in Java Leap Year Program in Java Addition Program in Java Number Pattern Programs in Java Star Pattern Programs in Java Package Program in Java Pyramid Program in Java Sorting Program in Java String Palindrome Program in Java Even Odd Program in Java For Loop Program in Java If Else Program in Java Switch Case Program in Java GCD Program in Java LCM Program in Java Hello Program in Java Matrix Program in Java Menu Driven Program in Java Series Program in Java Client Server Program in Java Swapping Program in Java Pig Latin Program in Java Tower of Hanoi Program in Java Recursion Program in Java Matrix Multiplication Program in Java Perfect Number Program in Java Classes and Objects in Java Example Programs String Programs in Java Array Programs in Java Constructor Program in Java Inheritance Program in Java Abstract class Program in Java Interface Program in Java Encapsulation Program in Java Polymorphism Program in Java Exception Handling Program in Java Multithreading Program in Java Thread Program in Java Collection Programs in Java ArrayList Program in Java Stack Program in Java Applet Program in Java Swing Program in Java JDBC Program in Java How to run Java program in command prompt How to run Java program in Eclipse Program to find and replace characters on string in java Program to find the duplicate characters in a string Program to check whether a given character is present in a string or not Java Program to Print Permutations of String Java program to find frequency of characters in a string Java Program to remove duplicate characters in a string

Java Sorting

Sorting Algorithms in Java Merge Sort in Java Quick Sort in Java Bubble Sort in Java Insertion Sort in Java Selection Sort in Java Heap Sort in Java Radix Sort in Java Topological Sort in Java Bucket Sort in Java Counting Sort in Java

Java OOPs Concepts

OOPs - Object Oriented Programming Objects and Classes in Java Methods in Java Java Naming Conventions Constructors in Java Java this keyword Java static keyword Inheritance in Java Aggregation in Java Java super keyword Constructor Chaining and Constructor Overloading Java Polymorphism Static and Dynamic Binding in Java Java Abstraction Abstract class in Java Interface in Java Difference between Abstract class and Interface Java final keyword Packages in Java Access Modifiers in Java Java Wrapper classes Java Numbers Java Characters Java Integer Java Boolean Java Arrays Java Command Line Arguments Java strictfp Keyword Java Math

Java Strings

Java Strings Java String Methods StringBuilder in Java StringBuffer in Java Java Regular Expressions StringBuffer vs StringBuilder String vs StringBuffer String vs StringBuilder String Manipulation in Java Java String Concatenation How to Reverse a String in Java String Array in Java How to Compare Two Strings in Java How to Concatenate Two Strings in Java Why String in Immutable in Java Java.lang.NumberFormatException for Input String String Pool in Java Java Generate Random String How to take String Input in Java Java String Interview Questions

Java Exceptions

Exception Handling in Java Java try catch Java throw Java throws Difference between throw and throws Java finally Java Custom Exception Java Exception Propagation

Garbage Collection

Automatic Resource Management in Java Java Garbage Collection Java finalize() Java gc() Difference between final, finally and finalize

Multithreading

Multithreading in Java Process and Thread in Java Basic Terms in Multithreading Java Thread creation Thread Scheduler in Java Java Thread class DeadLock in Java

Java IO

Java IO Java Read File Java file Reader Java Buffer Reader Java file Writer Java BufferedWriter Java InputStreamReader Scanner in Java Java StringReader Java StringReader Class Java PrintWriter Java File Java Read File Line By Line Java FileInputStream Java FileOutputStream Java Create File Java Delete File Java Open File Java Read File to String Java copy file Java Read JSON file Jar File in Java Java FileNotFoundException

Serialization

Java Serialization Java transient

Networking

Java Network Programming Java Socket Programming Java URL Java URLConnection HttpURLConnection in Java Java InetAddress Java DatagramSocket and Java DatagramPacket

AWT

Java AWT

Swing

Swing in Java

Java Collections

Collections in Java Java List Interface ArrayList in Java LinkedList in Java Vector in Java Stack in Java ArrayList vs LinkedList in Java ArrayList vs Vector in Java Java Set Interface HashSet in Java LinkedHashSet in Java TreeSet in Java Java Queue Interface PriorityQueue in Java ArrayDeque in Java Java Map Interface HashMap in Java LinkedHashMap in Java TreeMap in Java Dictionary in Java Hashtable in Java Properties in Java Collections class in Java Java Comparable Java Comparator Comparable vs Comparator in Java

Java Generics

Generics in Java

Java Annotations

Annotations in Java

Java JDBC

Java JDBC Tutorial JDBC Architecture Types of JDBC Drivers JDBC vs ODBC Java Database Connectivity with MySQL Statements in java Prepared statement in Java Resultset in java Java ResultSetMetaData DatabaseMetaData in Java Callable Statement in Java Transaction Management in java

Java Differences

Java vs JavaScript Python vs Java Kotlin vs Java Java vs C++ C# vs Java Static vs Non-static in Java C vs Java int vs Integer in Java Stack vs Heap in Java Java Array vs ArrayList

How to

How to run Java program How to set path in Java How to check the Java version in cmd How to install Java in Windows 10 How to run Java program in cmd How to add double quotes in a string in Java How to convert list to String in Java How to call a method in Java How to sort an array in Java How to iterate HashMap in Java How to write Java program How to create an array in Java How to create a package in Java How to generate random numbers in Java How to input String in Java How to create thread in Java How to find length of String in Java How to sort a string in Java How to use scanner in Java How to achieve multiple inheritance in Java How to find the length of an Array in Java How to run Java program in Eclipse How to call a function in Java How to create array of objects in Java How to create custom exception in Java How to import packages in Java How to run applet Program in Java How to take Array Input in Java How to achieve abstraction in Java How to call static method in Java How to compare characters in Java How to initialize string array in Java How to Install Java on MAC How to run java program in ubuntu How to find characters with the maximum number of times in a string java How to Set Java_home in Linux How to Split the String in Java with Delimiter How to Split String by Comma in Java How to remove special characters from String in Java How to remove last character from String in Java

Java 8 Features

Java 8 Features Lambda Expressions in Java Functional Interface in Java Streams in Java Java Base64 Encoding and Decoding Parallel Arrays Sort in Java

Java 9 Features

Java 9 Tutorial Java 9 Try With Resources Java 9 Interface Private Method

Java Servlet Tutorial

Java Servlets Tutorial

Java JSP Tutorial

Java JSP Tutorial

Hibernate Tutorial

Hibernate Tutorial

Spring Tutorial

Spring Tutorial

Spring MVC Tutorial

Spring MVC Tutorial

Jenkins Tutorial

Jenkins Tutorial

Java Math Methods

Math.abs() Math.acos() Math.addExact() Math.asin() Math.atan () Math.atan2() Math.cbrt() Math.ceil() Math.copysign() Math.cos() Math.cosh() Math.decrementExact() Math.exp() Math.expm1() Math.floor() Math.floorDiv() Math.floorMod() Math.getExponent() Math.hypot() Math.IEEEremainder() Math.incrementExact() Math.log() Math.log10() Math.log1p() Math.max() Math.min() Math.multiplyExact() Math.multiplyFull() Math.negateExact() Math.nextAfter() Math.nextDown() Math.nextUp() Math.pow() Math.random() Math.rint() Math.round() Math.scalb() Math.signum() Math.sin() Math.sinh() Math.sqrt() Math.subtractExact() Math.tan() Math.tanh() Math.toDegrees() Math.toIntExact() Math.toRadians() Math.ulp()

Java String Methods

toCharArray() copyValueOf() endsWith() equals() equalsIgnoreCase() format() getBytes() getChars() hashCode() indexOf() intern() isEmpty() join() lastIndexOf() length() replace() replaceAll() replaceFirst() split() startsWith() subSequence() substring() toLowerCase() toUpperCase() trim() valueOf()

Java Conversion

Java Convert String to int Java Convert int to String Java Convert String to long Java Convert long to String Java Convert String to float Java Convert float to String Java Convert String to double Java Convert double to String Java Convert String to Date Java Convert Date to String Java Convert String to Object Java Convert Object to String Java Convert String to char Java Convert char to String Java Convert int to long Java Convert long to int

Misc

Functional Interfaces in Java Singleton class in Java Awesome explanation of Strings in Java Object class in Java Static class in Java All the important string methods in Java String Handling Method in Java What are Array strings in Java Advantages and Disadvantages of Strings in Java Big Decimal class in Java Class definition in Java Char and String differences in Java Difference between String, StringBuffer and StringBuilder in java Replace character in string Java String Coding Interview Questions in Java What is String in Java? String isnullorempty in Java String Matches in Java Trim Method in String Java Bean class in Java Libraries in Java Arithmetic Operations on String in Java Convert Char array to string in java Check whether Java is installed or not How to calculate time difference in Java How to stop execution after a certain time in Java Jagged Array in Java Java ArraylistRemove() Time Complexity Java Swing Time Picker Zigzag Array in Java Array and String based questions in Java Array and String with Examples in Java Best Practices to use String Class in Java What is string in Java why it's immutable Java String Java String Inbuilt functions Java String Matches vs Contains Sum of digits in string in java Check the presence of Substring in a String in java Java import packages Interfaces and Classes in Strings in Java Maximum length of string in java Hidden classes in Java Class memory in Java public static void main string args meaning in java Reverse a String in Java String Concatenation in Java Difference between String and Char Array in Java Buffer reader to read string in Java Split String into String Array in Java Reverse a String using Collections in Java

Java Thread class

Thread class

The thread represents a part of the process. Every process can have multiple associated threads in which every thread may execute the same or different job. By default, each thread assigns a default priority by the JVM, which is used by thread scheduler to determine which thread must be run first. Thread class has various constructors and methods for creating and managing the behaviour of the threads.

 Thread class constructors:

  • Thread(): It creates a new Thread object.
  • Thread(Runnable target): It creates a new Thread object having a Runnable interface  as an argument.
  • Thread(Runnable target, String name): It creates a new Thread object having a Runnable target and String as an argument.
  • Thread(String name): It creates a new Thread object having String as an argument.
  • Thread(ThreadGroup group1, Runnable target1): It creates a new Thread object having Threadgroup and Runnable as an argument.
  • Thread(ThreadGroup group1, Runnable target1, String name1): It creates a new Thread object that has a specified name and targeted as its run object. The thread refers to the thread group referred to by the group1.
  • Thread(ThreadGroup grp, Runnable target2, String name1, long stackSize1): It creates a new Thread object having a target as its run object, has the specified name as its name1, the thread group(i.e., grp) have created thread and has the specified stack size1.
  • Thread(ThreadGroup group1, String name1): It creates a new thread object having Threadgroup and String as arguments.

Thread class Methods:

1. public String toString(): The toString() method of the Thread class is used to return the string representation of the thread, including the thread’s name, priority, and thread group.

Example:

public class Multithread implements Runnable   
 {   
 Thread t;  
 Multithread()   
 {  
 t = new Thread(this);  
  // this will call run() function   
  t.start();  
  }  
  public void run()   
  {  
  // returns a string representation of this thread    
  System.out.println(t.toString());  
  }   
  public static void main(String[] args)   
  {   
  new Multithread();  
  }   
 }   

Output:

Java Thread class

2. public void setContextClassLoader(ClassLoader classloader):

The context class loader will be the application’s class loader unless you explicitly change the thread’s context class loader. That means the context class loader can load the classes that application can load.

By using this method, we can set the context ClassLoader for the current thread. When a thread is created at that time, the context ClassLoader can be set.

Parameters:

Classloader: it is the context of ClassLoader for this Thread.

Exceptions:

SecurityException: This exception will occur if the current thread cannot set the context of ClassLoader.

3. public ClassLoader getContextClassLoader()

It returns the context ClassLoader of the current thread. If it returns null, it means it is indicating the system class loader or failing that the bootstrap class loader.

Example:

By using the setContextClassLoader() and  getContextClassLoader() we can set the  Context ClassLoader  and get the Context ClassLoader of the Thread.

public class Multithread implements Runnable {      
 Thread t;
 Multithread()
 {
 /*Passes the Runnable class object into the argument of the Thread class constructor.so that we can call start() method  of Thread class for running the run() method of the Runnable implemented class.*/ 
 t=new Thread(this);           
 t.start();
 }
 public void run()
 { 
 //It return the context ClassLoader of this Thread.
 ClassLoader c=t.getContextClassLoader();
 //It sets the context ClassLoader of this Thread.
 t.setContextClassLoader(c); 
 System.out.println("Class="+c.getClass());
 System.out.println("Parent="+c.getParent());
 }
 public static void main(String[] args) { 
 new Multithread();
 }
 } 

Output:

Java Thread class2

4. public final void setDaemon(boolean on)throws IllegalThreadStateException:

A thread can be set as daemon thread or a user thread. The Daemon thread is a low priority thread that runs in background to perform tasks such as garbage collection. The JVM terminates itself when all user threads finish their execution. The JVM does not have a concern that either a Daemon thread is running or not. Mostly background task is performed by the Daemon thread.

Parameters:

On:  It marks the thread as a daemon thread if it is true. It describes as user thread if it marks as false. 

If u have a thread t1, then t1.setDaemon(true) would make it Daemon thread.

t1.setDaemon(false) would make it user thread.

Exceptions:

IllegalThreadStateException- If this thread is alive.

5. public final boolean isDaemon():

It is used to test if the thread is a daemon thread or not. If the thread is a daemon, it returns true. Otherwise, it returns false.

Example:

Java program to demonstrate the way of working of the setDaemon() and isDaemon() method.

public class Multithread extends Thread {
 public Multithread(String name)
 {
 super(name);
 } 
 public void run()
 { 
 if(Thread.currentThread().isDaemon()) {
 System.out.println(getName()+"is Daemon thread");
 }
 else
 { 
 System.out.println(getName()+ "is User thread");
 }
 } 
 public static void main(String[] args) {
 Multithread t1=new Multithread("t1"); 
 Multithread t2=new Multithread("t2");
 Multithread t3=new Multithread("t3"); 
 t1.setDaemon(true);
 t1.start();
 t2.start(); 
 t3.setDaemon(true);
 t3.start();
 }
 } 

Output:

Java Thread class3

6. public final void setName(String name)

It changes the name of the thread with respect to the argument name.

Parameters:

name: It indicates the new name for the thread.

Exceptions:

SecurityException: If the current thread cannot change the thread name.

7. public final String getName()

It returns the current thread name.

Example:

import java.lang.*;
 public class Multithread implements Runnable {
  Thread t;
 public Multithread() {
  t = new Thread(this);
  // this will call run() function 
  t.start();
  } 
  public void run() {
 //sets the Thread name.
  t.setName("shifa");
  System.out.println("Thread name"+t);
  // prints thread name
  System.out.println("Thread = " + t.getName());
 } 
 public static void main(String[] args) {
 new Multithread();
 }
 } 

Output:

Java Thread class4

8. public final void setPriority(int prior)throws IllegalArgumentException:

 It changes the priority of the thread. A thread is assigned to the processor by the thread scheduler based on the priority of it. The thread always has some priority assigned to it by the JVM during its creation of the thread. The priority can either be given by the programmer explicitly or given by the JVM during the creation of the thread.

Parameters:

prior: It indicates the priority to be set for the thread.

Exceptions:

IllegalArgumentException: If the priority range is between MIN_PRIORITY to MAX_PRIORITY

9. public final int getPriority()

It returns the current thread priority.

Example: Using the setPriority() and getPriority() of the Thread.

import java.lang.*;
 public class Multithread extends Thread{
 public void run() {
 System.out.println("Inside run method");
  } 
 public static void main(String[] args) {
 Multithread t1= new Multithread();
 Multithread t2= new Multithread();
 System.out.println("t1 thread priority:"+t1.getPriority());
 System.out.println("t2 thread priority"+t2.getPriority());
 t1.setPriority(10); 
 t2.setPriority(5);
 System.out.println("After given the priority to each threads");
 System.out.println("t1 thread priority:"+t1.getPriority());
 System.out.println("t2 thread priority"+t2.getPriority());
 }
 } 

Output:

Java Thread class5

10. public static void sleep(long milliseconds1)throws InterruptedException:

It causes the currently executing thread to pause(sleep) for the specified number of milliseconds. Thread’s sleep() does not  cause to lose any monitors or locks, the current thread has acquired.

Parameters:

Milliseconds1: the length of time to sleep in milliseconds.

Exceptions:

InterruptedException:  It throws an exception when the thread is interrupted in the sleeping state by another thread.

11. public static void sleep(long  milliseconds1, int  nanoseconds1)throws InterruptedException:

It causes the currently executing thread to pause for the specified number of milliseconds1 and nanoseconds1. Thread’s sleep() does not cause to lose any monitors or locks, that the current thread has acquired.

Parameters:

Milliseconds1: the length of time to sleep in milliseconds.

Nanoseconds1: the time in a nanosecond to pause the thread.

Exceptions:

InterruptedException: It throws an exception when the thread is interrupted in the sleeping state by another thread.

Example:

public class Multithread {
 public static void main(String[] s1) throws InterruptedException {
 long start = System.currentTimeMillis();
 Thread.sleep(1000);
 Thread.sleep(1000,200);
 System.out.println("Sleep time in ms = "+(System.currentTimeMillis()-start)); 
 System.out.println("Sleep time in ms = "+(System.currentTimeMillis()-start));
 }
 } 

Output:

Java Thread class6

12. public void start()throws IllegalThreadStateException

Initially, It causes the thread to begin execution; then after the JVM calls the run() method of the thread for doing its task.

Exceptions:

IllegalThreadStateException: If the thread was already started.

13. public void run()

The complete working of the thread is written in the run() method. The run() method is called  usually using the start() method. The start() method call run() method for the execution of the thread.

Example:

public class Multithread extends Thread {
 public void run()
 {
 System.out.println("Current thread name:"+Thread.currentThread().getName()); 
 System.out.println("run() method called via start() method");
 }
 public static void main(String[] args) {
 Multithread t=new Multithread(); 
 t.start(); 
 } 
 } 

Output:

Java Thread class7

14. public static void yield()

This method causes the temporarily pause of the current thread and permit other threads to execute or complete its job. If the current executing thread is not doing anything important and if any other threads or processes need to be run at the same time, it is allowed to give permit that it should be run first than the current thread. Then the  current running thread is sent back to the Runnable state from the Running state.

Example:

class MyThread2 extends Thread
 { 
 public void run()
 {
 for(int i=0;i<5;i++) {
 System.out.println(Thread.currentThread().getName()+"in control");
 }
 }
 } 
 public class Multithread {
 public static void main(String[] args) {
  MyThread2 t=new MyThread2(); 
  t.start();
  for(int i=0;i<5;i++)
   {
  Thread.yield();
 System.out.println(Thread.currentThread().getName()+"in control");
   }
   }
 } 

Output:

Java Thread class8

15. public final void join()throws InterruptedException

The join() method is called ,when a  thread wants to wait until completing(die) the thread who called the join() method.

Exceptions:

InterruptedException: If any other thread has interrupted that thread who called the join()method.

16. public final synchronized void join(long millisecond)throws InterruptedException

The current thread waits until the thread on which it is called dead.

And also, the current thread waits in the specified time(milliseconds) for the thread dead, which calls the join method.

Parameters:

milliseconds: the time to wait in milliseconds.

Exceptions:

InterruptedException: If any thread is interrupted, thread who called the join() method.

17. public final synchronized void join(long milliseconds1, int nanoseconds1)throws InterruptedException

It causes the current thread on wait condition or sends the thread to the waiting state until the thread is dead on which join method is called, or the current thread waits for a specified time (milliseconds1+nanoseconds1) for the thread dead on which join method is called.

Parameters:

Milliseconds1+nanoseconds1:  The total time the thread has to wait for other threads.

Exceptions:

InterruptedException: If any thread is interrupted, the thread who called the join() method.

Example:

public class Multithread {
 public static void main(String[] args) {
  Thread thread1=new Thread(new Runnable1(),"thread1");
  Thread thread2=new Thread(new Runnable1(),"thread2");
  Thread thread3=new Thread(new Runnable1(),"thread3"); 
  thread1.start();
  //After 2 seconds wait or if the thread is dead second thread starts its execution.
   try
   {
  thread1.join(2000);
  } 
  catch(InterruptedException e)
  { 
 e.printStackTrace();
  }         
 thread2.start(); 
 //When first thread is dead then third thread starts.
 try
 {
 thread1.join(); 
 }catch(InterruptedException e)
 {
 e.printStackTrace();
 }
  thread3.start(); 
  //Before finishing main thread, all threads must be finished their execution.
 try
 { 
 thread1.join();
 thread2.join();
 thread3.join();
 }catch(InterruptedException e)
 { 
 e.printStackTrace();
 }
  System.out.println(“Before exiting main thread all threads are dead,");         
  }
 } 
 class Runnable1 implements Runnable{
 public void run()
 {
 System.out.println("Thread started"+Thread.currentThread().getName());
 try
 {
 Thread.sleep(4000);
 }
 catch(InterruptedException e)
 {
 e.printStackTrace();
 }
 System.out.println("Thread ended"+Thread.currentThread().getName());
 }
 } 

Output:

Java Thread class9

18. public boolean isInterrupted()

It is used to tests whether the thread has been interrupted or not. It returns true if this thread has been interrupted, otherwise return false.

19. public void interrupt()

This method is used to interrupt the thread. If any thread is in sleeping or waiting state, then using interrupt() method, we can interrupt the execution of that thread by showing InterruptedException.

Example:

class Thread1 extends Thread
 { 
 public void run()
 { 
 try 
 { 
 for(int i=0;i<5;i++) {
 Thread.sleep(1000);
 System.out.println("Shifa Thread1");
 }
 } 
 catch(InterruptedException e) {
 throw new RuntimeException("Thread Interrupted");
 }
 }
 }
 public class Multithread {
 public static void main(String[] args) {
 Thread1 t1=new Thread1(); 
 t1.setName("shifa Thread");
 t1.start();
 try
 {
 t1.interrupt();
 } 
 catch(Exception e)
 {
 System.out.println("Exception handled");
 }
 boolean a= t1.isInterrupted(); 
 System.out.println("Thread is interrupted or not "+a+"  "+"yes it is a interrupted thread ");
 }
 } 

Output:

Java Thread class10

20. public final boolean isAlive()

It tests whether the thread is alive or not. If thread is alive it returns true otherwise it returns false.

21. public Thread.State getState()

It returns the state of the thread, which called this method.

22. public long getId()

It returns the identifier of the current thread.

23. public static Thread currentThread()

The currently executing thread object is returned by the method.

Example:

class Thread1 extends Thread
 { 
 public void run()
 { 
 System.out.println("Shifa Thread1");
 }
 }
 public class Multithread {
 public static void main(String[] args) {
 Thread1 t1=new Thread1(); 
 Thread1 t2=new Thread1();
 t1.start();
 //It returns the state of the thread t1.
 System.out.println("t1 state ="+t1.getState()+" as start() method called before getState() method");
 //It returns the state of the thread t2.
 System.out.println("t2 state ="+t2.getState()+" as start() method called after getState() method");
 t2.start(); 
 System.out.println("current thread name ="+t1.currentThread());
 System.out.println("current thread name ="+t2.currentThread());
 System.out.println("t1 thread alive or not ="+t1.isAlive());
 System.out.println("t2 thread alive or not ="+t2.isAlive());
 System.out.println("t1 id is ="+t1.getId());
 System.out.println("t2 id is ="+t2.getId());
 }
 } 

Output:

Java Thread class11

24. public final ThreadGroup getThreadGroup()

It returns the thread group to which the thread belongs. ThreadGroup creates a group of threads. It offers a convenient way to manage groups of threads as a unit. This is particularly valuable in situation in which you want to suspend and resume a number of related threads.

25. public static int activeCount()

It returns an estimate of the number of active threads in the current thread’s thread group and in any other thread group that has the current thread’s thread group as an ancestor.

Example:

class Thread1 extends Thread
 { 
 Thread1(String threadname, ThreadGroup tgrp)
 {
 super(tgrp, threadname); 
 start();
 }
 public void run()
 { 
 for(int i=0;i<100;i++)
 {
 try
 { 
 Thread.sleep(10);
 }
 catch(InterruptedException ex)
 { 
 System.out.println("Exception encountered");
 }
 }
 }
 }
 public class Multithread {
  public static void main(String[] args) {
  //creating the ThreadGroup. 
 ThreadGroup threadgrp=new ThreadGroup("parent thread group");
  //Adding t1 thread into the ThreadGroup.
  Thread1 t1=new Thread1("one",threadgrp); 
  System.out.println("Starting first thread");
  //Adding t2 thread into the ThreadGroup.
  Thread1 t2=new Thread1("two",threadgrp);
  System.out.println("starting second thread");
  //checking the number of active thread.
  System.out.println("number of active thread in the ThreadGroup:"+threadgrp.activeCount()); 
  System.out.println("t1 thread belongs to the ThreadGroup  ="+t1.getThreadGroup());
  System.out.println("t2 thread belongs to the ThreadGroup  ="+t2.getThreadGroup());
     }       
 } 

Output:

Java Thread class12

26. public static int enumerate(Thread[] array1)

It is used to copy into the specified array every active thread in the current thread’s thread group and its subgroups.

Parameters:

array1: It returns the number of threads put into the array.

Example:

class Thread1 extends Thread
 { 
 Thread1(String thname, ThreadGroup tg)
 {
 super(tg,thname);
 start();
 } 
 public void run()
 {
 for(int i=0;i<5;i++)
 {
 try
 { 
 Thread.sleep(10);
 }
 catch(InterruptedException ex)
 {
 System.out.println("Exception encountered");
 } 
 System.out.println(Thread.currentThread().getName()+"completed exceuting");
 }
 }
 }
 public class Multithread { 
 public static void main(String[] args) {
 ThreadGroup thg1=new ThreadGroup("parent thread");
 ThreadGroup thg2=new ThreadGroup(thg1,"child thread");
 Thread1 t1=new Thread1("shifa Thread1",thg1);
 System.out.println("starting of Threda-1");
 Thread1 t2=new Thread1("shifa Thread2",thg2);
 System.out.println("starting of Threda-2");
 Thread[] group1=new Thread[thg1.activeCount()]; 
 int count=thg1.enumerate(group1);
 for(int i=0;i<count;i++)
 {
 System.out.println(group1[i].getName()+"found");
 }          
 }
 } 

Output:

Java Thread class13

27. public static Map<Thread, StackTracesElement[]> getAllStackTraces()

The stack traces map for all live threads is returned by the method. The threads are represented as threads and each map value represents an array of StackTraceElement that specifies the stack dump of the corresponding Thread.

Example:

import java.util.Map;
 public class Multithread implements Runnable{
 public void run()
 {
 System.out.println("This is run() method");
 } 
 public static void main(String[] args) {
 Multithread t1=new Multithread();
 Thread t=new Thread(t1);
 t.start();
 Map m1=Thread.getAllStackTraces();
 System.out.println(m1.toString());
 }
 } 

Output:

Java Thread class14

28. public final void suspend()

This method puts the thread from running to waiting state. This method is used if you want to stop the thread execution. This method allows a thread to temporarily cease execution. The suspended thread can be resumed using the resume() method.

29. public final void resume()

It is used to resume a thread which was suspended using suspend() method. This method allows the suspended thread to start again.

Example:

class Multithread1 implements Runnable{
 String name; // name of thread
 Thread t;
 Multithread1(String threadname) {
 name = threadname;
 t = new Thread(this, name); 
 System.out.println("New thread: " + t);
 t.start(); // Start the thread
 }
 // This is the entry point for thread.
 public void run() {
 try {
 for(int i = 7; i > 0; i--) { 
 System.out.println(name + ": " + i);
 Thread.sleep(200);
 }
 } catch (InterruptedException e) {
 System.out.println(name + " interrupted.");
 }
 System.out.println(name + " exiting.");
 }
 }
 public class Multithread {
 public static void main(String args[]) { 
 Multithread1 ob1 = new Multithread1("One");
 Multithread1 ob2 = new Multithread1("Two");
 try {
 Thread.sleep(1000);
 ob1.t.suspend(); 
 System.out.println("Suspending thread One");
 Thread.sleep(1000);
 ob1.t.resume();
 System.out.println("Resuming thread One");
 ob2.t.suspend(); 
 System.out.println("Suspending thread Two");
 Thread.sleep(1000); 
 ob2.t.resume();
 System.out.println("Resuming thread Two");
 } catch (InterruptedException e) {
 System.out.println("Main thread Interrupted");
 }
 // wait for threads to finish
 try { 
 System.out.println("Waiting for threads to finish.");
 ob1.t.join();
 ob2.t.join();
 } catch (InterruptedException e) {
 System.out.println("Main thread Interrupted");
 } 
 System.out.println("Main thread exiting.");
 }
 } 

Output:

Java Thread class15

UncaughtExceptionHandler:

Java handle Runtime(uncaught) Exceptions that we might not have handled in our program.

UncaughtException can be set (handle) at three levels.

  1. Thread.setDefaultUncaughtExceptionHandler
  2. Thread.setUncaughtExceptionHandler
  3. ThreadGroup.uncaughtException

Examples of Uncaught Exception:

30.  public static void setDefaultUncaughtExceptionHandler(Thread.UncaughtExceptionHandler uncatch_exec)

This method sets the default handler invoked, which arises when the thread terminates abruptly due to an uncaught exception, and no other handler has been defined for that thread.

Parameters:

uncatch_exec: The instance is used as the default uncaught exception handler. There is no default handler if it is null.

Example: Using Thread.setDefaultUncaughtExceptionHandler.

public class Multithread extends Thread {
 public static void main(String s1[])
 {
 Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler(){
 public void uncaughtException(Thread t,Throwable e)
 { 
 System.out.println(t.getName()+"thread end with following exception");
 System.out.println(e.getMessage());
 }
 });
 Thread t1=new Thread(new MyThread1(),"T1");
 t1.start();
 }
 } 
 class MyThread1 implements Runnable
 {
 public void run()
 {
 for(int i=1;i<=10;i++)
 { 
 System.out.println(Thread.currentThread().getName()+"i="+i);
 if(i==5)
 {
 throw new RuntimeException("My Runtime Exception....");
 }
 }
 } 
 } 

Output:

Java Thread class16

31. public void setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler excep_handler)

This method is used to set the handler called if any of the thread terminates abnormally due to uncaught exception if an exception arises.

Parameters:

excep_handler: It is the handler object to use when this thread terminates abnormally due to an uncaught exception.

Example: using Thread.setUncaughtExceptionHandler

public class Multithread extends Thread {
 public static void main(String s2[])throws Exception
 {
 Thread.currentThread().setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler(){ 
 public void uncaughtException(Thread t,Throwable e)
 {
 System.out.println(t.getName()+"thread end with following exception");
 System.out.println(e.getMessage());
 }
 }); 
 throw new Exception("exception thrown from somewhere in your program"); 
 }} 

Output:

Java Thread class17

32. public void uncaughtException(Thread t, Throwable e) 

This method is called by the Java Virtual Machine when a thread in this thread group stops because of an uncaught exception, and the thread does not have a specific Thread.UncaughtExceptionHandler installed.

Parameters:

The t: indicates that this is the thread that is about to exit.

The e: indicates this is the uncaught exception.

Example: Using the ThreadGroup.uncaughtException

public class Multithread extends Thread {
 public static void main(String s4[])throws Exception
 {
 MyThreadGroup myThreadGroup=new MyThreadGroup("myThreadGroup");
 Thread t1=new Thread(myThreadGroup, new MyThread1(),"T1"); 
 t1.start();
 }
 }
 class MyThreadGroup extends ThreadGroup
 { 
 public MyThreadGroup(String name)
 {
 super(name);
 }
 public void uncaughtException(Thread thread, Throwable t)
 { 
 ThreadGroup threadGroup=thread.getThreadGroup();
 System.out.println(threadGroup);
 System.out.println(thread.getName()+"thread end with following exception...."); 
 System.out.println(t.getMessage());
 }
 } 
 class MyThread1 implements Runnable
 {
  public void run()
  { 
  for(int i=1;i<=10;i++)
  {
  System.out.println(Thread.currentThread().getName()+" ,i="+i);
  if(i==5)
  { 
  throw new RuntimeException("My Runtime exception");
  }
 }
 }
 } 

Output:

Java Thread class18

33. public static Thread.UncaughtExceptionHandler getDefaultUncaughtExceptionHandler()

It returns the default handler invoked which arise if a thread abruptly terminates when there is an occurring an uncaught exception.

Example:

import java.lang.*;
 public class Multithread implements Runnable {
 Thread t;
 public Multithread() {
  t = new Thread(this); 
  // this will call run() function
  t.start();
    }
  public void run() {
  // prints thread name 
  System.out.println("Thread = " + t.getName());
   /*It returns the default handler invoked which arise if a thread abruptly         terminates when there is an occurring an uncaught exception. */
 Thread.UncaughtExceptionHandler handler = Thread .getDefaultUncaughtExceptionHandler(); 
  System.out.println(handler);
  } 
  public static void main(String[] args) {
  new Multithread(); 
 } 
 } 

Output:

Java Thread class19

34. public Thread.getUncaughtExceptionHandler getUncaughtExceptionHandler()

 It returns the handler invoked when this thread abruptly terminates due to an uncaught exception.

Example:

import java.lang.*;
 public class Multithread implements Runnable {
  Thread t;
 public Multithread() {
  t = new Thread(this);
  // this will call run() function
  t.start();
  } 
  public void run() {
  // prints thread name
  System.out.println("Thread = " + t.getName());
 /* It returns thehandler invoked which arise if a thread abruptly
          terminates when there is an occurring an uncaught exception.  */
  Thread.UncaughtExceptionHandler handler =  
  public static void main(String[] args) {
  new Multithread(); 
 new Multithread();
  } 
 } 

Output:

Java Thread class20



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