Why is object synchronization important in Java?

Synchronization of objects in Java is crucial to prevent thread safety issues such as data inconsistency, deadlock, and priority inversion for shared objects in a multi-threaded environment. Synchronization mechanisms include: 1) synchronization methods; 2) synchronization blocks; 3) lock objects. Synchronization ensures that a shared object is accessed by only one thread at a time, thereby maintaining data integrity and avoiding race conditions.

Why is object synchronization important in Java (with practical cases)

Overview

In a multi-threaded environment, multiple threads may access shared objects at the same time. Without synchronization, data inconsistencies, deadlocks, and other thread-safety issues can result.

The importance of synchronization

When multiple threads access shared objects at the same time, the following problems may occur:

• Inconsistent data: Threads may modify the same parts of the object, resulting in incorrect data.
• Deadlock: Threads may enter a wait state, waiting for other threads to release the lock, causing the application to stop responding.
• Priority inversion: Low-priority threads may block high-priority threads, thereby affecting application performance.

Synchronization mechanism

Java provides a variety of synchronization mechanisms to protect shared objects:

• Synchronization methods: Add the synchronized keyword to a method to acquire the object's lock during method execution.
• Synchronized blocks: Use synchronized blocks to restrict access to shared objects within a block of code to prevent other threads from accessing the block of code at the same time.
• Locks: Use the lock objects in the java.util.concurrent.locks package to provide finer control over objects.

Practical case

Consider the following bank account class:

class BankAccount {
    private double balance;

    public void deposit(double amount) {
        balance += amount;
    }

    public void withdraw(double amount) {
        balance -= amount;
    }

    public double getBalance() {
        return balance;
    }
}

In this class, deposit() There is no synchronization with the withdraw() method. If two threads call these methods at the same time, data inconsistency may result. For example, if one thread attempts to deposit $100 and another thread simultaneously attempts to withdraw $50, the account balance may be incorrectly updated to $49 instead of $50.

To solve this problem, we can use synchronized blocks to synchronize the deposit() and withdraw() methods:

public void deposit(double amount) {
    synchronized(this) {
        balance += amount;
    }
}

public void withdraw(double amount) {
    synchronized(this) {
        balance -= amount;
    }
}

Now, when two threads call these methods at the same time, they will acquire the object's lock and execute them sequentially. This will ensure that the data is consistent and no deadlocks occur.

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