Java ReentrantLock lock() Method

The lock() method of ReentrantLock class hold the lock if it is not held by another thread and returns immediately, and set the lock hold count to one.

Syntax

Parameter

No parameter is passed.

Returns

Does not have a return type.

Throws

No Exception is thrown.

Example 1

import java.text.SimpleDateFormat; 
import java.util.Date; 
import java.util.concurrent.ExecutorService; 
import java.util.concurrent.Executors; 
import java.util.concurrent.locks.ReentrantLock; 
  
class WorkerClassLL implements Runnable 
{ 
  String nm; 
  ReentrantLock relc; 
  public WorkerClassLL(ReentrantLock rl, String n) 
  { 
    relc = rl; 
    nm = n; 
  } 
  public void run() 
  { 
    boolean dn = false; 
    while (!dn) 
    { 
      //Outer Lock 
      boolean ans = relc.tryLock(); 
  
      //  True if lock is free 
      if(ans) 
      { 
        try
        { 
          int i=0;
          for(i=0;i<=6;i++) {
        	  
        	  if(i>=2)
        	  {
        		  relc.lock();
        		  Thread t = new Thread();
        		  System.out.println("Thread Created.....");
        		  if(i==3) {
        			  t.setName("Maint Thread2");
        			  System.out.println("Thread Created.....");
        		  }
        		
        		  
        	  }
        	  if(i==4)
        		  relc.unlock();
        		  break;
        	  
          }
          
          System.out.println(" after sleep(1500) Is locked - " + relc.isLocked()); 
          System.out.println("task name - " + nm + " work done"); 
  
          dn = true; 
        } 
        catch(Exception e) 
        { 
          e.printStackTrace(); 
        } 
        
      } 
      
      } 
    } 
  
  } 
   
public class ReentrantLocklockExample1 
{ 
  static final int MAX_Time = 2; 
  public static void main(String[] args) 
  { 
    ReentrantLock rel = new ReentrantLock(); 
    ExecutorService pool = Executors.newFixedThreadPool(MAX_Time); 
    Runnable wrk1 = new WorkerClassLL(rel, "Job1"); 
    pool.execute(wrk1); 
    pool.shutdown(); 
  } 
} 

Test it Now

Output:

after sleep(1500) Is locked - true
task name - Job1 work done

Example 2

import java.text.SimpleDateFormat; 
import java.util.Date; 
import java.util.concurrent.ExecutorService; 
import java.util.concurrent.Executors; 
import java.util.concurrent.locks.ReentrantLock; 
  
class WorkerClassC2 implements Runnable 
{ 
  String nm; 
  ReentrantLock relc; 
  public WorkerClassC2(ReentrantLock rl, String n) 
  { 
    relc = rl; 
    nm = n; 
  } 
  public void run() 
  { 
    boolean dn = false; 
    while (!dn) 
    { 
      //Outer Lock 
      boolean ans = relc.tryLock(); 
  
      //  True if lock is free 
      if(ans) 
      { 
        try
        { 
        	int i=1;
        	Thread t=new Thread();
          while(i<5) {
        	  
        	  System.out.println("     "+t.getThreadGroup());
        	  if(i==2)
            System.out.println("     "+t.getThreadGroup());
        	  if(i==3)
            System.out.println("     "+t.isInterrupted());
        	  if(i==4)
            System.out.println("     "+t.getStackTrace());
        	  
        	  i=i+1;
          }
        	  
         if(relc.isLocked())
         {
        	 
         }
         else {
        	 assert !relc.isHeldByCurrentThread();
             relc.lock();
         }
          
          System.out.println(" after sleep(1500) Is held by Current Thread - " + relc.isHeldByCurrentThread()); 
          System.out.println("task name - " + nm + " work done"); 
  
          dn = true; 
        } 
         
        finally {
        	relc.unlock();
        }     
      }     
      } 
    } 
  
  
  } 
 
  
public class ReentrantLocklockExample2 
{ 
  static final int MAX_Time = 2; 
  public static void main(String[] args) 
  { 
    ReentrantLock rel = new ReentrantLock(); 
    ExecutorService pool = Executors.newFixedThreadPool(MAX_Time); 
    Runnable wrk1 = new WorkerClassC2(rel, "Job1"); 
    pool.execute(wrk1); 
    pool.shutdown(); 
  } 
} 

Test it Now

Output:

java.lang.ThreadGroup[name=main,maxpri=10]
     java.lang.ThreadGroup[name=main,maxpri=10]
     java.lang.ThreadGroup[name=main,maxpri=10]
     java.lang.ThreadGroup[name=main,maxpri=10]
     false
     java.lang.ThreadGroup[name=main,maxpri=10]
     [Ljava.lang.StackTraceElement;@6bd19be0
 after sleep(1500) Is held by Current Thread - true
task name - Job1 work done

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