编写一个 Java 应用程序，该程序中有三个类： Triangle 、 Trapezoid 和 Circle 分别用来刻画"三角形"、"梯形"和"圆形"。具体要求如下： Triangle 类具有类型为 double 的三个边，以及周长、面积属性， Triangle 类具有返回周长、面积以及修改三个边的功能。此外， Triangle 类还有一个 boolean 型的属性，该属性用来判断三个数能够构成一个三角形。完成上述操作后，给 Triangle 再增加3个方法，分别用来返回3个边 sideA , sideB , sideC 的值。Lander 类具有类型为 double 的上底、下底、高、面积属性，具有返回面积的功能。 Circle 类具有类型为 double 的半径、周长和面积属性，具有返回周长、面积的功能。 编写一个测试类 Test ，分别创建类 Triangle 、 Trapezoid 和 Circle 的对象，并计算三角形、梯形和圆形的周长和面积。

好的，以下是 Java 代码实现：

Triangle 类：

public class Triangle {
    private double sideA;
    private double sideB;
    private double sideC;
    private double perimeter;
    private double area;
    private boolean isTriangle;

    public Triangle(double sideA, double sideB, double sideC) {
        this.sideA = sideA;
        this.sideB = sideB;
        this.sideC = sideC;
        this.isTriangle = (sideA + sideB > sideC) && (sideA + sideC > sideB) && (sideB + sideC > sideA);
        if (isTriangle) {
            this.perimeter = sideA + sideB + sideC;
            double p = this.perimeter / 2;
            this.area = Math.sqrt(p * (p - sideA) * (p - sideB) * (p - sideC));
        }
    }

    public boolean isTriangle() {
        return isTriangle;
    }

    public double getPerimeter() {
        return perimeter;
    }

    public void setPerimeter(double perimeter) {
        this.perimeter = perimeter;
    }

    public double getArea() {
        return area;
    }

    public void setArea(double area) {
        this.area = area;
    }

    public double getSideA() {
        return sideA;
    }

    public double getSideB() {
        return sideB;
    }

    public double getSideC() {
        return sideC;
    }

    public void setSideA(double sideA) {
        this.sideA = sideA;
        this.isTriangle = (sideA + sideB > sideC) && (sideA + sideC > sideB) && (sideB + sideC > sideA);
        if (isTriangle) {
            this.perimeter = sideA + sideB + sideC;
            double p = this.perimeter / 2;
            this.area = Math.sqrt(p * (p - sideA) * (p - sideB) * (p - sideC));
        }
    }

    public void setSideB(double sideB) {
        this.sideB = sideB;
        this.isTriangle = (sideA + sideB > sideC) && (sideA + sideC > sideB) && (sideB + sideC > sideA);
        if (isTriangle) {
            this.perimeter = sideA + sideB + sideC;
            double p = this.perimeter / 2;
            this.area = Math.sqrt(p * (p - sideA) * (p - sideB) * (p - sideC));
        }
    }

    public void setSideC(double sideC) {
        this.sideC = sideC;
        this.isTriangle = (sideA + sideB > sideC) && (sideA + sideC > sideB) && (sideB + sideC > sideA);
        if (isTriangle) {
            this.perimeter = sideA + sideB + sideC;
            double p = this.perimeter / 2;
            this.area = Math.sqrt(p * (p - sideA) * (p - sideB) * (p - sideC));
        }
    }
}

Trapezoid 类：

public class Trapezoid {
    private double top;
    private double bottom;
    private double height;
    private double area;

    public Trapezoid(double top, double bottom, double height) {
        this.top = top;
        this.bottom = bottom;
        this.height = height;
        this.area = (top + bottom) * height / 2;
    }

    public double getTop() {
        return top;
    }

    public void setTop(double top) {
        this.top = top;
        this.area = (top + bottom) * height / 2;
    }

    public double getBottom() {
        return bottom;
    }

    public void setBottom(double bottom) {
        this.bottom = bottom;
        this.area = (top + bottom) * height / 2;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
        this.area = (top + bottom) * height / 2;
    }

    public double getArea() {
        return area;
    }

    public void setArea(double area) {
        this.area = area;
    }
}

Circle 类：

public class Circle {
    private double radius;
    private double circumference;
    private double area;

    public Circle(double radius) {
        this.radius = radius;
        this.circumference = 2 * Math.PI * radius;
        this.area = Math.PI * radius * radius;
    }

    public double getRadius() {
        return radius;
    }

    public void setRadius(double radius) {
        this.radius = radius;
        this.circumference = 2 * Math.PI * radius;
        this.area = Math.PI * radius * radius;
    }

    public double getCircumference() {
        return circumference;
    }

    public double getArea() {
        return area;
    }

    public void setArea(double area) {
        this.area = area;
    }
}

Test 类：

public class Test {
    public static void main(String[] args) {
        Triangle triangle = new Triangle(3, 4, 5);
        if (triangle.isTriangle()) {
            System.out.println("Triangle perimeter: " + triangle.getPerimeter());
            System.out.println("Triangle area: " + triangle.getArea());
        } else {
            System.out.println("Not a triangle.");
        }

        Trapezoid trapezoid = new Trapezoid(3, 5, 4);
        System.out.println("Trapezoid area: " + trapezoid.getArea());

        Circle circle = new Circle(2.5);
        System.out.println("Circle circumference: " + circle.getCircumference());
        System.out.println("Circle area: " + circle.getArea());
    }
}

以上是三个类和测试类的实现。在测试类中分别创建 Triangle 、 Trapezoid 和 Circle 的对象，并计算周长和面积。其中 Triangle 类中增加了修改三个边的方法 setSideA()、setSideB() 和 setSideC()，其他两个类中增加了修改面积的方法 setArea()。