2.修改Triangle类,重新定义为TriangleWithException类。 调用TriangleWithException类的构造方法，如果创建的三角形的违反了规则，抛出一个IllegalTriangleException异常。

下面是修改后的 TriangleWithException 类：

public class TriangleWithException {
    private double sideA;
    private double sideB;
    private double sideC;

    public TriangleWithException() {
        sideA = 1;
        sideB = 1;
        sideC = 1;
    }

    public TriangleWithException(double s1, double s2, double s3) throws IllegalTriangleException {
        if (isInvalid(s1, s2, s3)) {
            throw new IllegalTriangleException(s1, s2, s3);
        }
        sideA = s1;
        sideB = s2;
        sideC = s3;
    }

    public double getA() {
        return sideA;
    }

    public double getB() {
        return sideB;
    }

    public double getC() {
        return sideC;
    }

    public void setABC(double s1, double s2, double s3) throws IllegalTriangleException {
        if (isInvalid(s1, s2, s3)) {
            throw new IllegalTriangleException(s1, s2, s3);
        }
        sideA = s1;
        sideB = s2;
        sideC = s3;
    }

    public boolean isInvalid(double s1, double s2, double s3) {
        return ((s1 + s2 <= s3) || (s1 + s3 <= s2) || (s2 + s3 <= s1) || s1 <= 0 || s2 <= 0 || s3 <= 0);
    }

    public double getArea() {
        double s = (sideA + sideB + sideC) / 2;
        return Math.pow(s * (s - sideA) * (s - sideB) * (s - sideC), 0.5);
    }

    public double getPerimeter() {
        return sideA + sideB + sideC;
    }

    @Override
    public String toString() {
        return "The triangle: sideA = " + sideA + " , " + "sideB = " + sideB + " , " +
                "sideC = " + sideC + "\n" +
                "the area is " + getArea() + "\n" +
                "the perimeter is " + getPerimeter();
    }
}

在 TriangleWithException 类中，我们新增了一个叫做 IllegalTriangleException 的异常类，用于在创建三角形时抛出异常。在构造函数和 setABC 方法中，我们加入了对三角形是否合法的判断，如果不合法，则抛出 IllegalTriangleException 异常，否则正常赋值。