Better singleton implement for android/java platform. It's based on android.util.Singleton

XSingleton.java

public abstract class XSingleton<T> {

    private T mInstance;

    protected abstract T create();

    /**
     * is this object ready for work?
     * That means is this object has been init by JVM.
     * This method is design for The Double Checked Lock Broken
     * (see this: https://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html )
     *
     * @return ready or not
     */
    protected abstract boolean ready(T target);

    public final T get() {
        if (mInstance != null
                && ready(mInstance)) {
            return mInstance;
        }

        synchronized (this) {
            if (mInstance == null) {
                mInstance = create();
            }
            return mInstance;
        }
    }
}

// usage for caller
public class SingletonFoo extends XSingleton<Foo> {


    @Override
    protected Foo create() {
        return new Foo();
    }

    @Override
    protected boolean ready(Foo target) {
        return target.getFoo() != null;
    }
}


// Target to be singled.
public class Foo {
    private String foo;

    public String getFoo() {
        return foo;
    }
}