Problem
You are given a class with synchronized method A, and a normal method C. If you have two threads in one instance of a program, can they call A at the same time? Can they call A and C at the same time?
Solution:
Java provides two ways to achieve synchronization: synchronized method and synchronized statement.
Synchronized method: Methods of a class which need to be synchronized are declared with “synchronized” keyword. If one thread is executing a synchronized method, all other threads which want to execute any of the synchronized methods on the same objects get blocked.
Syntax: method1 and method2 need to be synchronized
public class SynchronizedMethod { // Variables declaration public synchronized T Method1() { // Statements } public synchronized T method2() { // Statements } // Other methods }T is return type.
Synchronized statement: It provides the synchronization for a group of statements rather than a method as a whole It needs to provide the object on which these synchronized statements will be applied, unlike in a synchronized method
Syntax: synchronized statements on “this” object
synchronized(this) { // statement 1 // ... // statement N }
i) If you have two threads in one instance of a program, can they call A at the same time?
Not possible; read the above paragraph.
ii) Can they call A and C at the same time?
Yes. Only methods of the same object which are declared with the keyword synchronized can’t be interleaved
References