Break Singleton Design Pattern

Author: DhirajGadekar

Creational Design Pattern/SingletonDesignPattern/bin/BreakSingleton/throughreflection/AlreadyExistException.class

@@ -0,0 +1,9 @@
+package BreakSingleton.throughreflection;
+
+public class AlreadyExistException extends RuntimeException {
+
+    public AlreadyExistException(String msg) {
+
+        super(msg);
+    }
+}

Creational Design Pattern/SingletonDesignPattern/bin/BreakSingleton/throughreflection/Main.class

@@ -0,0 +1,25 @@
+package BreakSingleton.throughreflection;
+
+import java.lang.reflect.Constructor;
+
+public class Main {
+    
+    /**
+     * @param args
+     */
+    public static void main(String[] args) {
+
+        Singleton s1 = Singleton.getIntance();
+        Singleton s2 = null;
+        try {
+            Constructor<Singleton> constructor = Singleton.class.getDeclaredConstructor();
+            constructor.setAccessible(true);
+            s2 = constructor.newInstance();
+        } catch (Exception e) {
+            
+            e.printStackTrace();
+        }
+        System.out.println(s1.hashCode());
+        System.out.println(s2.hashCode());
+    }
+}

Creational Design Pattern/SingletonDesignPattern/bin/BreakSingleton/throughreflection/Singleton.class

@@ -0,0 +1,26 @@
+package BreakSingleton.throughreflection;
+
+public class Singleton {
+    
+    private static Singleton s;
+    private Singleton() {
+        if(s != null) {
+
+            throw new AlreadyExistException("Instance Already Exists");
+        }
+    }
+
+    public static Singleton getIntance() {
+        if(s == null) {
+
+            synchronized(Singleton.class) {
+
+                if(s == null) {
+
+                    s = new Singleton();
+                }
+            }
+        }
+        return s;
+    }
+}

Creational Design Pattern/SingletonDesignPattern/bin/BreakSingleton/throughserialization/Main.class

@@ -0,0 +1,44 @@
+package BreakSingleton.throughserialization;
+
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+
+public class Main {
+    public static void main(String[] args) {
+        
+        Singleton s1 = Singleton.getInstance();
+        Singleton s2 = null;
+        try {
+
+            FileOutputStream fos = new FileOutputStream("singleton.do");
+            ObjectOutputStream oos = new ObjectOutputStream(fos);
+
+            oos.writeObject(s1);
+
+            fos.close();
+            oos.close();
+        } catch(Exception e) {
+
+            e.printStackTrace();
+        }
+
+        try {
+
+            FileInputStream fis = new FileInputStream("singleton.do");
+            ObjectInputStream ois = new ObjectInputStream(fis);
+            
+            s2 = (Singleton)ois.readObject();
+
+            fis.close();
+            ois.close();
+        } catch(Exception e) {
+
+            e.printStackTrace();
+        }
+
+        System.out.println(s1.hashCode());
+        System.out.println(s2.hashCode());
+    }
+}

Creational Design Pattern/SingletonDesignPattern/bin/BreakSingleton/throughserialization/Singleton.class

@@ -0,0 +1,33 @@
+package BreakSingleton.throughserialization;
+
+import java.io.Serializable;
+import BreakSingleton.throughreflection.AlreadyExistException;
+
+public class Singleton implements Serializable {
+    private static Singleton s;
+    private Singleton() {
+
+        if(s != null) {
+
+            throw new AlreadyExistException("Instance already exist");
+        }
+    }
+    public static Singleton getInstance() {
+
+        if(s == null) {
+
+            synchronized(Singleton.class) {
+                
+                if(s == null) {
+
+                    s = new Singleton();
+                }
+            }
+        }
+        return s;
+    }
+    public Object readResolve() {
+
+        return s;
+    }
+}