Lesson: Design Patterns

                                                                    Singleton 

-- Constructor protected olduqda, o zaman singleton design pattern-i qirmaq olur. Bunun ucun araliq bir class yaradiriq ve esas class-i extend edirik.

package org.singleton;

public class Test {

    private static Test test = null;

    private Test() {}

    public static Test getInstance() {
        if(test == null)
            test = new Test();
        return test;
    }
}

package com.example.ms7.creational_patterns;

public final class Singleton {
    private static Singleton instance;

    private Singleton() {
    }

    public static synchronized Singleton getInstance() {
        if (instance == null) {
            synchronized (Singleton.class) {
                if (instance == null)
                    instance = new Singleton();
            }
        }
        return instance;
    }
}

-- Immutable class

package org.singleton;

public class Teacher {
    public String name;
}

package org.singleton;

public class Person {

    private static Person person = null;

    private Teacher t = null;

    private Person() {
    }

    public Person(Teacher t) {
        this.t = t;
    }

    public static Person instance() {
        if (person == null)
            person = new Person();
        return person;
    }

    public Teacher getM() {
        Teacher tt = new Teacher();
        tt.name = t.name;
        return tt;
    }
}

package org.singleton;

public class Main {
    public static void main(String[] args) {
        Teacher mercedes = new Teacher();
        Person person = new Person(mercedes);
        mercedes.name = "abc";

        System.out.println(person.getM().name);

        person.getM().name = "asdfasdf";
        System.out.println(person.getM().name);
    }
}