有个程序不明白解决思路

有个程序不明白
package cha4;
public interface QuadInterface{
public double b24ac();
public void x1x2();
}





package cha4;
public class QuadImp11 implements QuadInterface{
private double[] abc;
private double[] x1x2 = new double[2];
double rb24ac;

QuadImp11(double[] newAbc){
abc = newAbc;
rb24ac = b24ac();
}
public double b24ac(){
return abc[1] * abc[1] - 4 * abc[0] * abc[2];
}

public double x1x2(){
if(rb24ac == 0){
x1x2[0] = (-abc[1]) / (2*abc[0]);
x1x2[1] = x1x2[0];
}
else
if(rb24ac > 0){
x1x2[0] = (-abc[1] - Math.sqrt(rb24ac)) / (2 * abc[0]);
x1x2[1] = (-abc[1] + Math.sqrt(rb24ac)) / (2 * abc[0]);
}

else{
System.out.println("No real Roots!");
}
//return 1;

}

public double getX1() { return x1x2[1]; }
public double getX2() { return x1x2[0]; }
public void displayX1X2(){
if(rb24ac >= 0){
System.out.println("x1 = "+x1x2[0]);
System.out.println("x2 = "+x1x2[1]);
}
}
}



这两个程序书上的要求是接口QuadInterface的第一个实现类QuadImp11

都打完了，第二个程序结果是
--------------------Configuration: <Default>--------------------
E:\course\Java\第四章\QuadImp11.java:2: cha4.QuadImp11 不是抽象的，并且未覆盖 cha4.QuadInterface 中的抽象方法 x1x2()
public class QuadImp11 implements QuadInterface{
  ^
E:\course\Java\第四章\QuadImp11.java:15: cha4.QuadImp11 中的 x1x2() 无法实现 cha4.QuadInterface 中的 x1x2()；正在尝试使用不兼容的返回类型
找到： double
需要： void
  public double x1x2(){
  ^
2 错误

Process completed.


请各位帮忙看下，谢谢了

[解决办法]

Java code

public interface QuadInterface{public void x1x2();//返回类型是void，而你在下面实现时，变成了double类型，这不是重写}public class QuadImp11 implements QuadInterface{public double x1x2(){}}
[解决办法]
Java code
//自己再添加一个public class, 包含main 方法interface QuadInterface {    public double b24ac();    public void x1x2();}class QuadImp11 implements QuadInterface {    private double[] abc;    private double[] x1x2 = new double[2];    double rb24ac;    QuadImp11(double[] newAbc) {        abc = newAbc;        rb24ac = b24ac();    }    public double b24ac() {        return abc[1] * abc[1] - 4 * abc[0] * abc[2];    }    public void x1x2() {        if (rb24ac == 0) {            x1x2[0] = (-abc[1]) / (2 * abc[0]);            x1x2[1] = x1x2[0];        } else if (rb24ac > 0) {            x1x2[0] = (-abc[1] - Math.sqrt(rb24ac)) / (2 * abc[0]);            x1x2[1] = (-abc[1] + Math.sqrt(rb24ac)) / (2 * abc[0]);        }        else {            System.out.println("No real Roots!");        }        // return 1;    }    public double getX1() {        return x1x2[1];    }    public double getX2() {        return x1x2[0];    }    public void displayX1X2() {        if (rb24ac >= 0) {            System.out.println("x1 = " + x1x2[0]);            System.out.println("x2 = " + x1x2[1]);        }    }}
[解决办法]
Java code
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