定义一个Triangle类表示三角形，其中三个double型变量a、b、c表示三条边长。为该类定义两个构造方法:默认构造方法设置三角形的三条边长都为0.0; 带三个参数的构造方法通过传递三个参数创建三角形对象。定义求三角形面积的方法area), 面积计算公式为area=Math.sqrt(s*(s- -a)(s b)(-)),其中s-(a+b+e)/2。编写另一个程序测试这个三角形类的所有方法。

好的，这里是Triangle类的代码实现：

public class Triangle {
    private double a;
    private double b;
    private double c;

    public Triangle() {
        this.a = 0.0;
        this.b = 0.0;
        this.c = 0.0;
    }

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

    public double getA() {
        return a;
    }

    public void setA(double a) {
        this.a = a;
    }

    public double getB() {
        return b;
    }

    public void setB(double b) {
        this.b = b;
    }

    public double getC() {
        return c;
    }

    public void setC(double c) {
        this.c = c;
    }

    public double area() {
        double s = (a + b + c) / 2.0;
        double area = Math.sqrt(s * (s - a) * (s - b) * (s - c));
        return area;
    }
}

这里是测试程序的代码：

public class TestTriangle {
    public static void main(String[] args) {
        Triangle t1 = new Triangle();
        System.out.println("Triangle 1: a = " + t1.getA() + ", b = " + t1.getB() + ", c = " + t1.getC() + ", area = " + t1.area());

        Triangle t2 = new Triangle(3.0, 4.0, 5.0);
        System.out.println("Triangle 2: a = " + t2.getA() + ", b = " + t2.getB() + ", c = " + t2.getC() + ", area = " + t2.area());

        t1.setA(6.0);
        t1.setB(8.0);
        t1.setC(10.0);
        System.out.println("Triangle 1: a = " + t1.getA() + ", b = " + t1.getB() + ", c = " + t1.getC() + ", area = " + t1.area());
    }
}

运行结果如下：

Triangle 1: a = 0.0, b = 0.0, c = 0.0, area = 0.0
Triangle 2: a = 3.0, b = 4.0, c = 5.0, area = 6.0
Triangle 1: a = 6.0, b = 8.0, c = 10.0, area = 24.0

其中，Triangle类有两个构造方法，一个默认的无参构造方法和一个带三个参数的构造方法。area方法计算三角形面积，测试程序中创建了两个Triangle对象t1和t2，并分别调用了它们的构造方法和area方法。最后，通过set方法修改了t1的三条边长，并再次调用area方法计算面积。