public class SingletonClass {<br /> private static final SingletonClass SINGLE_INSTANCE = new SingletonClass();<br /> private SingletonClass() {}<br /> public static SingletonClass getInstance() {<br /> return SINGLE_INSTANCE;<br /> }<br /> }

– A private constructor<br /> – A static field containing its only instance<br /> – A static factory method for obtaining the instance</p> <p>public final class ClassSingleton<br /> {</p> <p> private static ClassSingleton INSTANCE;<br /> private String info = “Initial info class”;</p> <p> private ClassSingleton()<br /> {<br /> }</p> <p> public static ClassSingleton getInstance()<br /> {<br /> if(INSTANCE == null)<br /> {<br /> INSTANCE = new ClassSingleton();<br /> }</p> <p> return INSTANCE;<br /> }</p> <p> // getters and setters<br /> }</p> <p> =============Usage============</p> <p>To use our ClassSingleton, we simply need to get the instance statically:</p> <p>ClassSingleton classSingleton1 = ClassSingleton.getInstance();</p> <p>System.out.println(classSingleton1.getInfo()); //Initial class info</p> <p>ClassSingleton classSingleton2 = ClassSingleton.getInstance();<br /> classSingleton2.setInfo(“New class info”);</p> <p>System.out.println(classSingleton1.getInfo()); //New class info<br /> System.out.println(classSingleton2.getInfo()); //New class info<br />

public class SingletonOnDemand {</p> <p> private SingletonOnDemand () {}<br /> private static class Singleton {<br /> private static final SingletonOnDemand instance = new SingletonOnDemand();<br /> }</p> <p> public static SingletonOnDemand getInstance () {<br /> System.out.println(“create instance”);<br /> return Singleton.instance;<br /> }<br /> }

public class DB {<br /> // champs de l’objet</p> <p> private DB(){<br /> // initialisation des champs<br /> }</p> <p> private static final DB INSTANCE = new DB();<br /> public static DB getInstance(){<br /> return INSTANCE;<br /> }<br /> }

public final class SomeSingleton {<br /> public static final SomeSingleton INSTANCE;</p> <p> private SomeSingleton() {<br /> INSTANCE = (SomeSingleton)this;<br /> System.out.println(“init complete”);<br /> }</p> <p> static {<br /> new SomeSingleton();<br /> }<br /> }

class SingletonExample {</p> <p> // private field that refers to the object<br /> private static SingletonExample singleObject;</p> <p> private SingletonExample() {<br /> // constructor of the SingletonExample class<br /> }</p> <p> public static SingletonExample getInstance() {<br /> // write code that allows us to create only one object<br /> // access the object as per our need<br /> }<br /> }

class SingletonExample {</p> <p> // private field that refers to the object<br /> private static SingletonExample singleObject;</p> <p> private SingletonExample() {<br /> // constructor of the SingletonExample class<br /> }</p> <p> public static SingletonExample getInstance() {<br /> // write code that allows us to create only one object<br /> // access the object as per our need<br /> }<br /> }

synchoronized