Java synchronized keyword examples

<method modifier> synchronized <method signature> {
    // synchronized code block
}

synchronized (expression) {
    // synchronized code block
}

Some Rules about synchronized keyword:

-          The expression must be evaluated to a reference type, i.e an object reference.

-          The current executing thread will try to acquire a lock before executes the synchronized code block:

• • • • • For synchronized statement: the monitor associates with the object returns by the expression.
        • For synchronized method:
          • • If the method is static, the lock associates with the Class object of the class in which the method is declared.
            • If the method is non-static, the lock associates with this – the object for which the method is invoked.

-          If the lock is not acquired by any thread, the current executing thread will own the lock and execute the synchronized code block.

-          While the current executing thread owns the lock, no other threads can acquire that lock.

-          When the synchronized code block completes, the current executing thread releases the lock.

-          There is no something called “synchronized constructor”.

Java synchronized keyword Examples:

class Counter {
    private static int count;
    static synchronized void increase() {
        count++;
    }
}

class BankAccount {
    private double balance;
    synchronized void withdraw(double amount) {
        this.balance -= amount;
    }
    synchronized void deposit(double amount) {
        this.balance += amount;
    }
}

Object lock = new Object();
synchronized (lock) {
    System.out.println("Synchronized statement");
}

Related Topics:

• Java Synchronization Tutorial

Other Recommended Tutorials:

• 9 Rules about Constructors in Java
• 12 Rules and Examples About Inheritance in Java
• 12 Rules of Overriding in Java You Should Know
• 10 Java Core Best Practices Every Java Programmer Should Know
• Understand Interfaces in Java
• Understand how variables are passed in Java
• Understand encapsulation in Java

About the Author:

Nam Ha Minh is certified Java programmer (SCJP and SCWCD). He began programming with Java back in the days of Java 1.4 and has been passionate about it ever since. You can connect with him on Facebook and watch his Java videos on YouTube.