Static Classes In Java

Question

Is there anything like static class in java?

What is the meaning of such a class. Do all the methods of the static class need to be static too?

Is it required the other way round, that if a class contains all the static methods, shall the class be static too?

What are static classes good for?

Answer 1

Java has static nested classes but it sounds like you're looking for a top-level static class. Java has no way of making a top-level class static but you can simulate a static class like this:

• Declare your class final - Prevents extension of the class since extending a static class makes no sense
• Make the constructor private - Prevents instantiation by client code as it makes no sense to instantiate a static class
• Make all the members and functions of the class static - Since the class cannot be instantiated no instance methods can be called or instance fields accessed
• Note that the compiler will not prevent you from declaring an instance (non-static) member. The issue will only show up if you attempt to call the instance member

Simple example per suggestions from above:

public class TestMyStaticClass {      public static void main(String []args){         MyStaticClass.setMyStaticMember(5);         System.out.println("Static value: " + MyStaticClass.getMyStaticMember());         System.out.println("Value squared: " + MyStaticClass.squareMyStaticMember());         // MyStaticClass x = new MyStaticClass(); // results in compile time error      } }  // A top-level Java class mimicking static class behavior public final class MyStaticClass {     private MyStaticClass () { // private constructor         myStaticMember = 1;     }     private static int myStaticMember;     public static void setMyStaticMember(int val) {         myStaticMember = val;     }     public static int getMyStaticMember() {         return myStaticMember;     }     public static int squareMyStaticMember() {         return myStaticMember * myStaticMember;     } } 

What good are static classes? A good use of a static class is in defining one-off, utility and/or library classes where instantiation would not make sense. A great example is the Math class that contains some mathematical constants such as PI and E and simply provides mathematical calculations. Requiring instantiation in such a case would be unnecessary and confusing. See the Math class and source code. Notice that it is final and all of its members are static. If Java allowed top-level classes to be declared static then the Math class would indeed be static.