返回对具有静态方法和静态字段的类的引用，而无需实例化

Question

I want to create a wrapper class that calls static methods and member fields from a class that is provided by a library I am unable to view the code.

This is to avoid boilerplate setting code of the global member fields when I need to use a static method in a specific context.

I want to try to avoid creating wrapper methods for each static method.

My question:

Is it possible to return a class with static methods from a method to access just the static methods without instantiating it?

Code is below with comments in-line.

The code is used to demonstrate a change in a static value when the method getMath() is invoked.

I want to avoid the setting of the value before calling the static method.

StaticMath.setFirstNumber(1);
StaticMath.calc(1);

StaticMath.setFirstNumber(2);
StaticMath.calc(1);

I am using the Eclipse IDE and it comes up with Warnings, which I understand, but want to avoid.

I tried searching for something on this subject, so if anyone can provide a link I can close this.

public class Demo {
    // Static Methods in a class library I don't have access to. 
    static class StaticMath {
        private static int firstNum;

        private StaticMath() {  
        }

        public static int calc(int secondNum) {
            return firstNum + secondNum;
        }

        public static void setFirstNumber(int firstNum) {
            StaticMath.firstNum = firstNum;
        }
    }

    // Concrete Class
    static class MathBook {
        private int firstNum;

        public MathBook(int firstNum) {
            this.firstNum = firstNum;
        }

        // Non-static method that gets the class with the static methods.
        public StaticMath getMath() {
            StaticMath.setFirstNumber(firstNum);
            // I don't want to instantiate the class.
            return new StaticMath();
        }
    }

    public static void main(String... args) {
        MathBook m1 = new MathBook(1);
        MathBook m2 = new MathBook(2);

        // I want to avoid the "static-access" warning.
        // Answer is 2
        System.out.println(String.valueOf(m1.getMath().calc(1)));
        // Answer is 3
        System.out.println(String.valueOf(m2.getMath().calc(1)));
    }
}

Answer 1

I'd just wrap it to make for an atomic operation:

public static class MyMath{

    public static synchronized int myCalc( int num1 , int num2 ){
         StaticMath.setFirstNum(num1);
         return StaticMath.calc(num2);
    }

}

Drawback: You'll have to make sure, StaticMath is not used avoiding this "bridging" class.

Usage:

int result1 = MyMath.myCalc( 1, 1 );
int result1 = MyMath.myCalc( 2, 1 );

Answer 2

You shouldnt call a static method through an object reference. You should directly use class reference to call a static method like this:

StaticMath.calc(1)

But if you still need it for some reason, you can return null in getMath method, but you will still get warning in Eclipse:

public StaticMath getMath() {
    StaticMath.setFirstNumber(firstNum);
    return null;
}

Answer 3

I infer that question is not properly asked if the answer is not

   StaticMath.calc(1)

Other issue you may be facing due to package visibility to static inner classes. Which is a design choice by the writer of Demo class. If you can mark your classes MathBook and StaticMath public then you can access them like below:

   Demo.StaticMath.calc(1);