//【例4-14】  方法覆蓋的使用和父類中被覆蓋方法的調(diào)用。
//程序清單4-14:  MethodOverrideDemo.java
package e4_14;

public class MethodOverrideDemo {
	public static void main(String args[]) {
		// 創(chuàng)建一元二次方程實(shí)例：5x^2+6x+1 = 0;
		TwoVariableEquation twe = new TwoVariableEquation(5, 6, 1);
		// 求解兩實(shí)根x1,x2
		System.out.println("twe.getX1() = " + twe.getX1());
		System.out.println("twe.getX2() = " + twe.getX2());
	}
}

// 一元一次方程類OneVariableEquation
class OneVariableEquation {
	double a;

	double b;

	public OneVariableEquation(double a, double b) {
		this.a = a;
		this.b = b;
	}

	public void setAB(double a, double b) {
		this.a = a;
		this.b = b;
	}

	double getX1() {
		return -b / a;
	}
}

// 一元二次方程類TwoVariableEquation繼承類OneVariableEquation
class TwoVariableEquation extends OneVariableEquation {
	double c;

	public TwoVariableEquation(double a, double b, double c) {
		// 調(diào)用父類的構(gòu)造方法public OneVariableEquation(double a, double b)
		super(a, b);
		this.c = c;
	}

	public void setABC(double a, double b, double c) {
		// 調(diào)用繼承自父類的方法public void setAB(double a, double b)
		setAB(a, b);
		this.c = c;
	}

	// 子類中覆蓋方法可以擴(kuò)大而不能縮小父類中被覆蓋方法的訪問控制權(quán)限，
	// 此處“getX1()”可為public、protected和默認(rèn)，而不能為private
	public double getX1() {// 覆蓋父類方法
		// 用"super.<方法名>([實(shí)參表])"調(diào)用被子類覆蓋的方法getX1()
		return super.getX1() / 2 + Math.sqrt(Math.pow(b, 2) - 4 * a * c);
	}

	public double getX2() {
		return super.getX1() / 2 - Math.sqrt(Math.pow(b, 2) - 4 * a * c);
	}
}