From b94e1882aeadc54eb260504c7fdc3376431b751e Mon Sep 17 00:00:00 2001
From: Nilesh Ghone <33826370+Nilesh-Ghone@users.noreply.github.com>
Date: Tue, 25 Oct 2022 13:41:39 +0530
Subject: [PATCH] added singleton-design-pattern java programs

---
 .../EagerInitializedSingleton.java            | 19 +++++++++++++
 .../LazyInitializedSingleton.java             | 21 +++++++++++++++
 .../StaticBlockSingleton.java                 | 27 +++++++++++++++++++
 .../ThreadSafeSingleton.java                  | 22 +++++++++++++++
 4 files changed, 89 insertions(+)
 create mode 100644 Java/singleton-design-pattern/EagerInitializedSingleton.java
 create mode 100644 Java/singleton-design-pattern/LazyInitializedSingleton.java
 create mode 100644 Java/singleton-design-pattern/StaticBlockSingleton.java
 create mode 100644 Java/singleton-design-pattern/ThreadSafeSingleton.java

diff --git a/Java/singleton-design-pattern/EagerInitializedSingleton.java b/Java/singleton-design-pattern/EagerInitializedSingleton.java
new file mode 100644
index 0000000..0d3b9c9
--- /dev/null
+++ b/Java/singleton-design-pattern/EagerInitializedSingleton.java
@@ -0,0 +1,19 @@
+public class EagerInitializedSingleton {
+    
+    private static final EagerInitializedSingleton instance = new EagerInitializedSingleton();
+    
+    //private constructor to avoid client applications to use constructor
+    private EagerInitializedSingleton(){}
+
+    public static EagerInitializedSingleton getInstance(){
+        return instance;
+    }
+	
+	public void test() {
+		System.out.println("This is Singleton instance");
+	}
+	
+	public static void main(String[] args) {
+		EagerInitializedSingleton.getInstance().test();
+	}
+}
\ No newline at end of file
diff --git a/Java/singleton-design-pattern/LazyInitializedSingleton.java b/Java/singleton-design-pattern/LazyInitializedSingleton.java
new file mode 100644
index 0000000..f2b5a12
--- /dev/null
+++ b/Java/singleton-design-pattern/LazyInitializedSingleton.java
@@ -0,0 +1,21 @@
+public class LazyInitializedSingleton {
+
+    private static LazyInitializedSingleton instance;
+    
+    private LazyInitializedSingleton(){}
+    
+    public static LazyInitializedSingleton getInstance(){
+        if(instance == null){
+            instance = new LazyInitializedSingleton();
+        }
+        return instance;
+    }
+	
+	public void test() {
+		System.out.println("This is LazyInitializedSingleton instance");
+	}
+	
+	public static void main(String[] args) {
+		LazyInitializedSingleton.getInstance().test();
+	}
+}
\ No newline at end of file
diff --git a/Java/singleton-design-pattern/StaticBlockSingleton.java b/Java/singleton-design-pattern/StaticBlockSingleton.java
new file mode 100644
index 0000000..6b89b70
--- /dev/null
+++ b/Java/singleton-design-pattern/StaticBlockSingleton.java
@@ -0,0 +1,27 @@
+public class StaticBlockSingleton {
+
+    private static StaticBlockSingleton instance;
+    
+    private StaticBlockSingleton(){}
+    
+    //static block initialization for exception handling
+    static{
+        try{
+            instance = new StaticBlockSingleton();
+        }catch(Exception e){
+            throw new RuntimeException("Exception occured in creating singleton instance");
+        }
+    }
+    
+    public static StaticBlockSingleton getInstance(){
+        return instance;
+    }
+	
+	public void test() {
+		System.out.println("This is StaticBlockSingleton instance");
+	}
+	
+	public static void main(String[] args) {
+		StaticBlockSingleton.getInstance().test();
+	}
+}
\ No newline at end of file
diff --git a/Java/singleton-design-pattern/ThreadSafeSingleton.java b/Java/singleton-design-pattern/ThreadSafeSingleton.java
new file mode 100644
index 0000000..87a5672
--- /dev/null
+++ b/Java/singleton-design-pattern/ThreadSafeSingleton.java
@@ -0,0 +1,22 @@
+public class ThreadSafeSingleton {
+
+    private static ThreadSafeSingleton instance;
+    
+    private ThreadSafeSingleton(){}
+    
+    public static synchronized ThreadSafeSingleton getInstance(){
+        if(instance == null){
+            instance = new ThreadSafeSingleton();
+        }
+        return instance;
+    }
+	
+	public void test() {
+		System.out.println("This is ThreadSafeSingleton instance");
+	}
+	
+	public static void main(String[] args) {
+		ThreadSafeSingleton.getInstance().test();
+	}
+    
+}
\ No newline at end of file