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?
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:
final
- Prevents extension of the class since extending a static class makes no senseprivate
- Prevents instantiation by client code as it makes no sense to instantiate a static classstatic
- Since the class cannot be instantiated no instance methods can be called or instance fields accessedSimple 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.