1Z1-804 Real Exam Prep DEMO

Question 10: Which two properly implement a Singleton pattern?
A.class Singleton {
private static Singleton instance;
private Singleton () {}
public static synchronized Singleton getInstance() {
if (instance == null) {
instance = new Singleton ();
}
return instance;
}
}
B.class Singleton {
private static Singleton instance = new Singleton();
protected Singleton () {}
public static Singleton getInstance () {
return instance;
}
}
C.class Singleton {
Singleton () {}
private static class SingletonHolder {
private static final Singleton INSTANCE = new Singleton ();
}
public static Singleton getInstance () {
return SingletonHolder.INSTANCE; } }
D.enum Singleton {
INSTANCE;
}
Correct Answer: A,D
Explanation:
A: Here the method for getting the reference to the SingleTon object is correct.
B: The constructor should be private
C: The constructor should be private
Note: Java has several design patterns Singleton Pattern being the most commonly used. Java
Singleton pattern belongs to the family of design patterns, that govern the instantiation process. This
design pattern proposes that at any time there can only be one instance of a singleton (object)
created by the JVM.
The class's default constructor is made private, which prevents the direct instantiation of the object
by others (Other Classes). A static modifier is applied to the instance method that returns the object
as it then makes this method a class level method that can be accessed without creating an object.
OPTION A == SHOW THE LAZY initialization WITHOUT DOUBLE CHECKED LOCKING TECHNIQUE ,BUT
ITS CORRECT OPTION D == Serialzation and thraead-safety guaranteed and with couple of line of code
enum Singleton pattern is best way to create Singleton in Java 5 world.
AND THERE ARE 5 WAY TO CREATE SINGLETON CLASS IN JAVA 1>>LAZY LOADING (initialization)
USING SYCHRONIZATION 2>>CLASS LOADING (initialization) USING private static final Singleton
instance = new
Singleton(); 3>>USING ENUM 4>>USING STATIC NESTED CLASS
5>>USING STATIC BLOCK
AND MAKE CONSTRUCTOR PRIVATE IN ALL 5 WAY.