편집 기록

package Calc;

import java.util.Scanner;

class Calculator{
    int a,b;
    void setOprands(int a,int b) {
        this.a = a;
        this.b = b;
    }
    int sum() {
        return this.a+this.b;
    }
    void plus() {

    }
    void minus() {
    }
    void run() {
        plus();
        minus();
    }
}
class plus extends Calculator{
    void plus() {
        System.out.println("++"+sum());
    }

}

class minus extends Calculator{
    void minus() {
        System.out.println("--"+sum());
    }
}

public class CalculatorConstructorDemo4 {

    public static void main(String[] args) {
        Calculator Calc = new Calculator();
        Calculator plus1 = new plus();
        Calculator minus1 = new minus();
        Scanner a = new Scanner(System.in);
        Scanner b = new Scanner(System.in);
        //Calc.setOprands(a.nextInt(), b.nextInt());
        Calc.setOprands(10, 20);
        plus1.plus();
        minus1.minus();
    }

}

질문은 간단합니다. 위의코드를 돌리면

결과로 나타날 숫자가 0으로 나타나는데,

왜 sum메소드 연산이 안되는 건가요?

package Calc;

import java.util.Scanner;

class Calculator{ int a,b; void setOprands(int a,int b) { this.a = a; this.b = b; } int sum() { return this.a+this.b; } void plus() {

}
void minus() {
}
void run() {
    plus();
    minus();
}

} class plus extends Calculator{ void plus() { System.out.println("++"+sum()); }

}

class minus extends Calculator{ void minus() { System.out.println("--"+sum()); } }

public class CalculatorConstructorDemo4 {

public static void main(String[] args) {
    Calculator Calc = new Calculator();
    Calculator plus1 = new plus();
    Calculator minus1 = new minus();
    Scanner a = new Scanner(System.in);
    Scanner b = new Scanner(System.in);
    //Calc.setOprands(a.nextInt(), b.nextInt());
    Calc.setOprands(10, 20);
    plus1.plus();
    minus1.minus();
}

}

질문은 간단합니다. 위의코드를 돌리면

결과로 나타날 숫자가 0으로 나타나는데,

왜 sum메소드 연산이 안되는 건가요?