class TestSave implements Serializable {

    static final long serialVersionUID = 42L;

    private static class SingleClass{
        static TestSave getInstance = new TestSave();
    }
    private TestSave(){}

    static TestSave getInstance(){return SingleClass.getInstance;}

    Object readResolve() throws Exception{
        return SingleClass.getInstance;
    }
}

 TestSave testSave = TestSave.getInstance();
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream("TestSaveFile"));
        objectOutputStream.writeObject(testSave);

        ObjectInputStream inputStream = new ObjectInputStream(new FileInputStream("TestSaveFile"));
        Object cc = inputStream.readObject();
        System.out.println(testSave == cc);   // true