Java Threads

How to create a thread in java program?

create a thread by instantiating an object of type Thread class.

What are the ways to create a thread in java program?

• Implement the Runnable interface
• Extend the Thread class

How to create a thread using Runnable interface?

// Create a thread by implementing Runnable interface in java program                                              
class ChildThread implements Runnable {                                         
 Thread thr;                                                                    
 ChildThread() {                                                                
  thr = new Thread(this, "Child Thread Task");                                  
  System.out.println("Child thread: " + thr);                                   
  //starts child thread here                                                    
  thr.start();                                                                  
 }                                                                              
 public void run() {                                                            
  try {                                                                         
   int i = 0;                                                                   
   while( i <= 4) {                                                             
    System.out.println("Child thread i: " + i);                                 
    Thread.sleep(600);                                                          
    i++;                                                                        
   }                                                                            
  } catch(InterruptedException ex) {                                            
    System.out.println("Child thread is interrupted.");                         
  }                                                                             
  System.out.println("Child thread is completed");                              
 }                                                                              
}                                                                               
                                                                                
class ThreadTest {                                                              
 public static void main(String args[]) {                                       
  // Creates the child thread                                                   
  new ChildThread();                                                            
                                                                                
  try {                                                                         
   int i = 0;                                                                   
   while( i <= 4) {                                                             
    System.out.println("Main thread i: " + i);                                  
    Thread.sleep(900);                                                          
    i++;                                                                        
   }                                                                            
  } catch(InterruptedException ex) {                                            
    System.out.println("Main thread is interrupted.");                          
  }                                                                             
  System.out.println("Main thread is completed");                               
 }                                                                              
}   

Output:

$ javac ThreadTest.java
$ java ThreadTest
Child thread: Thread[Child Thread Task,5,main]
Main thread i: 0
Child thread i: 0
Child thread i: 1
Main thread i: 1
Child thread i: 2
Main thread i: 2
Child thread i: 3
Child thread i: 4
Main thread i: 3
Child thread is completed
Main thread i: 4
Main thread is completed

How to create a thread using Thread class?

// Create a thread by extending Thread class in java program                                              
class ChildThread extends Thread {                                              
 ChildThread() {                                                                
  super("Child Thread Task");                                                   
  System.out.println("Child thread: " + this);                                  
  //starts child thread here                                                    
  start();                                                                      
 }                                                                              
 public void run() {                                                            
  try {                                                                         
   int i = 0;                                                                   
   while( i <= 4) {                                                             
    System.out.println("Child thread i: " + i);                                 
    Thread.sleep(600);                                                          
    i++;                                                                        
   }                                                                            
  } catch(InterruptedException ex) {                                            
    System.out.println("Child thread is interrupted.");                         
  }                                                                             
  System.out.println("Child thread is completed");                              
 }                                                                              
}                                                                               
                                                                                
class ExtendThreadTest {                                                        
 public static void main(String args[]) {                                       
  // Creates the child thread                                                   
  new ChildThread();                                                            
                                                                                
  try {                                                                         
   int i = 0;                                                                   
   while( i <= 4) {                                                             
    System.out.println("Main thread i: " + i);                                  
    Thread.sleep(900);                                                          
    i++;                                                                        
   }                                                                            
  } catch(InterruptedException ex) {                                            
    System.out.println("Main thread is interrupted.");                          
  }                                                                             
  System.out.println("Main thread is completed");                               
 }                                                                              
}   

Output:

Child thread: Thread[Child Thread Task,5,main]
Main thread i: 0
Child thread i: 0
Child thread i: 1
Main thread i: 1
Child thread i: 2
Main thread i: 2
Child thread i: 3
Child thread i: 4
Main thread i: 3
Child thread is completed
Main thread i: 4
Main thread is completed

How to create a multiple threads in java program?

// Multiple Threads creation in java program                                    
class ChildThread implements Runnable {                                         
 Thread thr;                                                                    
 String threadName;                                                             
 ChildThread(String name) {                                                     
  threadName = name;                                                            
  thr = new Thread(this, threadName);                                           
  System.out.println(threadName + "- Child thread: " + thr);                    
  //starts child thread here                                                    
  thr.start();                                                                  
 }                                                                              
 public void run() {                                                            
  try {                                                                         
   int i = 0;                                                                   
   while( i <= 4) {                                                             
    System.out.println(threadName + "- Child thread i: " + i);                  
    Thread.sleep(600);                                                          
    i++;                                                                        
   }                                                                            
  } catch(InterruptedException ex) {                                            
    System.out.println(threadName + "- Child thread is interrupted.");          
  }                                                                             
  System.out.println(threadName + "- Child thread is completed");               
 }                                                                              
}                                                                               
                                                                                
class MultipleThreadTest {                                                      
 public static void main(String args[]) {                                       
  // Creates the child thread                                                   
  new ChildThread("one");                                                       
  new ChildThread("two");                                                       
                                                                                
  try {                                                                         
   int i = 0;                                                                   
   while( i <= 4) {                                                             
    System.out.println("Main thread i: " + i);                                  
    Thread.sleep(900);                                                          
    i++;                                                                        
   }                                                                            
  } catch(InterruptedException ex) {                                            
    System.out.println("Main thread is interrupted.");                          
  }                                                                             
  System.out.println("Main thread is completed");                               
 }                                                                              
}   

Output:

$ javac MultipleThreadTest.java 
$ java MultipleThreadTest
one- Child thread: Thread[one,5,main]
two- Child thread: Thread[two,5,main]
one- Child thread i: 0
Main thread i: 0
two- Child thread i: 0
one- Child thread i: 1
two- Child thread i: 1
Main thread i: 1
one- Child thread i: 2
two- Child thread i: 2
Main thread i: 2
one- Child thread i: 3
two- Child thread i: 3
one- Child thread i: 4
two- Child thread i: 4
Main thread i: 3
one- Child thread is completed
two- Child thread is completed
Main thread i: 4
Main thread is completed

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