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Where and how can I create a private constructor in Java?
We can use a private contractor in a Java while creating a singleton class. The Singleton's purpose is to control object creation, limiting the number of objects to only one. Since there is only one Singleton instance, any instance fields of a Singleton will occur only once per class, just like static fields. Singletons often control access to resources, such as database connections or sockets.
Example
The easiest implementation consists of a private constructor and a field to hold its result, and a static accessor method with a name like getInstance().
The private field can be assigned from within a static initializer block or, more simply, using an initializer. The getInstance( ) method (which must be public) then simply returns this instance –
public class SingletonSample {
private static SingletonSample singleton = new SingletonSample();
private SingletonSample() { }
public static SingletonSample getInstance() {
return singleton;
}
protected static void demoMethod( ) {
System.out.println("demoMethod for singleton");
}
public static void main(String[] args) {
SingletonSample tmp = SingletonSample.getInstance( );
tmp.demoMethod( );
}
}Output
demoMethod for singleton
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