What does this code, what does "if" followed return statement [duplicate]

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• What does return do when used inside an if statement? 8 answers

I want to know what is going to do the if statement when is followed by return statement like this.

public static boolean running = false;
public Thread gameThread;

public synchronized void start(){
    if (running)return; // Here. 
       running = true; 
       gameThread = new Thread();
       gameThread.start();
}