Synchronized Blocks

Unlike synchronized methods, a synchronized block allows targeting a specific block of code inside a method and choosing which object's monitor to lock on. This reduces lock contention and improves throughput.

Fine-Grained Locking

In synchronized methods, the lock target is always this (or the class object). With synchronized blocks, you specify the target:

synchronized (lockObject) {
    // Critical section code
}

This allows creating private lock objects (private final Object lock = new Object();). Locking on private objects prevents external clients from locking on your instance monitor, eliminating potential lock hijacking.

Code Walkthrough

This class demonstrates two independent operations protected by distinct private locks to allow parallel updates.

public class FineGrainedLockingDemo {
    private int count1 = 0;
    private int count2 = 0;
private final Object lock1 = new Object();
    private final Object lock2 = new Object();
public void increment1() {
        // Only synchronize the write operation
        synchronized (lock1) {
            count1++;
        }
    }
public void increment2() {
        synchronized (lock2) {
            count2++;
        }
    }
}

Interview-Relevant Information