SingletonSample.java

public class SingletonSample{

    private static SingletonSample instance= null;
    private static Object mutex= new Object();

    private String value;

    private SingletonSample(){}

    public static SingletonSample getInstance(){
        if (instance == null) {
            synchronized (mutex) {
                if(instance == null) instance= new SingletonSample();
            }
        }

        return instance;
    }

    public synchronized void setter(String value) {
        this.value = value;
    }

    public synchronized String getter() {
        return value;
    }
}