상속

package inherited;

public class CalculatorDemo {
	public static void main(String[] args) {
		SubtractionableCalcultor c1 = new SubtractionableCalcultor();
		c1.setOperands(10,  20);
		c1.sum();
		c1.avg();
		c1.subtract();
	}
}

class Calculator {
	int left, right;
	
	public void setOperands(int left, int right) {
		this.left = left;
		this.right = right;
	}
	
	public void sum() {
		System.out.println(this.left + this.right);
	}
	
	public void avg() {
		System.out.println((this.left + this.right) / 2);
	}
}

class SubtractionableCalcultor extends Calculator {
	public void subtract() {
		System.out.println(this.left - this.right);
	}
}

new를 통해 생성한 객체(클래스)가 상속한 클래스의 메소드나 변수를 가져다 쓸 수 있다.