Singleton class vs static methods and fields?

Why are Singleton Classes used in Android/Java, when the same functionality looks to be provided by using a class with static fields and methods?

e.g.

public class StaticClass {
    private static int foo = 0;

    public static void setFoo(int f) {
        foo = f;
    }

    public static int getFoo() {
        return foo;
    }
}

vs

public class SingletonClass implements Serializable {

    private static volatile SingletonClass sSoleInstance;
    private int foo;

    //private constructor.
    private SingletonClass(){

        //Prevent form the reflection api.
        if (sSoleInstance != null){
            throw new RuntimeException("Use getInstance() method to get the single instance of this class.");
        }

        foo = 0;
    }

    public static SingletonClass getInstance() {
        if (sSoleInstance == null) { //if there is no instance available... create new one
            synchronized (SingletonClass.class) {
                if (sSoleInstance == null) sSoleInstance = new SingletonClass();
            }
        }

        return sSoleInstance;
    }

    //Make singleton from serialize and deserialize operation.
    protected SingletonClass readResolve() {
        return getInstance();
    }

    public void setFoo(int foo) {
        this.foo = foo;
    }

    public int getFoo() {
        return foo;
    }
}