How to avoid deadlock in Java Threads

What is deadlock ?

 When two or more threads waiting for each other to release lock and get stuck for infinite time , situation is called deadlock . it will only happen in case of multitasking.

How do you detect deadlock in Java ?
 

if nested synchronized block or calling one synchronized method from other or trying to get lock on different object then there is good chance of deadlock if developer is not very careful.

write code which will result in deadlock ?

public void method1(){
synchronized(String.class){
System.out.println("Aquired lock on String.class object");

synchronized (Integer.class) {
System.out.println("Aquired lock on Integer.class object");
}
}
}

public void method2(){
synchronized(Integer.class){
System.out.println("Aquired lock on Integer.class object");

synchronized (String.class) {
System.out.println("Aquired lock on String.class object");
}
}
}

How to avoid deadlock in Java ?

 

public void method1(){
synchronized(Integer.class){
System.out.println("Aquired lock on Integer.class object");

synchronized (String.class) {
System.out.println("Aquired lock on String.class object");
}
}
}

public void method2(){
synchronized(Integer.class){
System.out.println("Aquired lock on Integer.class object");

synchronized (String.class) {
System.out.println("Aquired lock on String.class object");
}
}
}

 
Now there would not be any deadlock because both method is accessing lock on Integer and String object in same order . so if thread A acquires lock on Integer object , thread B will not proceed until thread A releases Integer lock , same way thread A will not be blocked even if thread B holds String lock because now thread B will not expect thread A to release Integer lock to proceed further.