In Java, thread synchronization is the process of controlling the access to shared resources by multiple threads to avoid race conditions and ensure data consistency. Synchronization is important because multiple threads executing concurrently can lead to inconsistent or incorrect results.

To synchronize access to a shared resource, you can use the synchronized keyword. This keyword can be used in two ways:

1. Synchronized methods: You can declare a method as synchronized, which means that only one thread can execute the method at a time.

public synchronized void myMethod() {
    // code that accesses shared resources
}

2. Synchronized blocks: You can also use synchronized blocks to control access to shared resources. A synchronized block is a block of code that is enclosed in a synchronized statement, and it can be used to synchronize access to a specific object.

public void myMethod() {
    synchronized(sharedObject) {
        // code that accesses shared resources
    }
}

In this example, the synchronized statement is synchronized on the sharedObject, which means that only one thread at a time can execute the block of code enclosed in the statement.

When a thread enters a synchronized method or block, it acquires the lock associated with the object being synchronized on. The lock is released when the thread exits the synchronized method or block.

By synchronizing access to shared resources, you can prevent race conditions and ensure that data consistency is maintained. However, it's important to use synchronization judiciously, as excessive synchronization can lead to performance issues and even deadlocks.