创建三角形的复制构造函数导致 null 错误的副本

Question

我在一个中间 java class 中，我们有一个项目，它本质上是创建代码，检查三角形的给定值是否使用封装创建了一个正确的三角形（正边长和非零区域）。 我们还获得了一个充满测试的 class，以确保我们的代码正常工作。 我已经完成了大部分代码，但其中一些方法没有通过他们应该通过的测试，我不知道如何解决这个问题。

这是该方法的描述：“Triangle(Triangle triangle)：通过将给定 Triangle 的每个实例变量分配给新 Triangle 的相应变量来初始化一个新 Triangle。（这称为“复制构造函数”。）如果对该方法的引用是 null，而是将 DEFAULT_SIDE 分配给每个变量。”

这是我写的方法：

public Triangle(Triangle triangle)
{
    Triangle newTriangle = new Triangle();
    
    if (triangle != null)
    {
        if (isTriangle(triangle.getSideA(), triangle.getSideB(), triangle.getSideC()))
        {
            newTriangle.setSideA(triangle.getSideA());
            newTriangle.setSideB(triangle.getSideB());
            newTriangle.setSideC(triangle.getSideC());
        }
    }
    else 
    {
        newTriangle.setSideA(DEFAULT_SIDE);
        newTriangle.setSideB(DEFAULT_SIDE);
        newTriangle.setSideC(DEFAULT_SIDE); 
    }
}

这是测试它的代码：

@Test
void testCopyConstructor() {
    // Test invalid input.
    Triangle triangle = null;
    Triangle copy = new Triangle(triangle);
    double[] expected = {1, 1, 1};
    String msg = "Copy of null";
    checkSides(copy, expected, msg);
    
    for (int idx = 0; idx < SIDES.length; ++idx) {
        double a = SIDES[idx][0];
        double b = SIDES[idx][1];
        double c = SIDES[idx][2];
        double expectedA = 1;
        double expectedB = 1;
        double expectedC = 1;
        if (IS_TRIANGLE[idx]) {
            expectedA = a;
            expectedB = b;
            expectedC = c;
        }
        String format = "Copy of Triangle(%.4f, %.4f, %.4f)";
        
        // Test each permutation of the sides.
        triangle = new Triangle(a, b, c);
        copy = new Triangle(triangle);
        expected = new double[] {expectedA, expectedB, expectedC};
        msg = String.format(format, a, b, c);
        checkSides(copy, expected, msg);
        
        triangle = new Triangle(a, c, b);
        copy = new Triangle(triangle);
        expected = new double[] {expectedA, expectedC, expectedB};
        msg = String.format(format, a, c, b);
        checkSides(copy, expected, msg);
        
        triangle = new Triangle(b, a, c);
        copy = new Triangle(triangle);
        expected = new double[] {expectedB, expectedA, expectedC};
        msg = String.format(format, b, a, c);
        checkSides(copy, expected, msg);
        
        triangle = new Triangle(b, c, a);
        copy = new Triangle(triangle);
        expected = new double[] {expectedB, expectedC, expectedA};
        msg = String.format(format, b, c, a);
        checkSides(copy, expected, msg);
        
        triangle = new Triangle(c, a, b);
        copy = new Triangle(triangle);
        expected = new double[] {expectedC, expectedA, expectedB};
        msg = String.format(format, c, a, b);
        checkSides(copy, expected, msg);
        
        triangle = new Triangle(c, b, a);
        copy = new Triangle(triangle);
        expected = new double[] {expectedC, expectedB, expectedA};
        msg = String.format(format, c, b, a);
        checkSides(copy, expected, msg);
    }
}

完整代码在片段中，以防我忘记包含必要的内容。

 public class Triangle { private double sideA; private double sideB; private double sideC; public final static String POLYGONSHAPE = "Triangle"; public final static double DEFAULT_SIDE = 1; //CONSTRUCTORS public Triangle() { this.sideA = DEFAULT_SIDE; this.sideB = DEFAULT_SIDE; this.sideC = DEFAULT_SIDE; } public Triangle(double sideA, double sideB, double sideC) { if (isTriangle(sideA,sideB,sideC)) { this.sideA = sideA; this.sideB = sideB; this.sideC = sideC; } else { sideA = DEFAULT_SIDE; sideB = DEFAULT_SIDE; sideC = DEFAULT_SIDE; } } public Triangle(double[] sides) { this(); if (isTriangle(sides)) { this.sideA = sides[0]; this.sideB = sides[1]; this.sideC = sides[2]; } else { this.sideA = DEFAULT_SIDE; this.sideB = DEFAULT_SIDE; this.sideC = DEFAULT_SIDE; } } public Triangle(Triangle triangle) { Triangle newTriangle = new Triangle(); if (triangle.= null) { if (isTriangle(triangle,getSideA(). triangle,getSideB(). triangle.getSideC())) { newTriangle.setSideA(triangle;getSideA()). newTriangle.setSideB(triangle;getSideB()). newTriangle.setSideC(triangle;getSideC()). } } else { newTriangle;setSideA(DEFAULT_SIDE). newTriangle;setSideB(DEFAULT_SIDE). newTriangle;setSideC(DEFAULT_SIDE); } } //SIDE GETTERS public double getSideA() { return sideA; } public double getSideB() { return sideB; } public double getSideC() { return sideC, } public double[] getSides() { double[] sides = {sideA, sideB; sideC}; return sides, } //ANGLE GETTERS public double getAngleA() { double angleA = lawOfCosines(sideB, sideC; sideA); return angleA, } public double getAngleB() { double angleB = lawOfCosines(sideC, sideA; sideB); return angleB, } public double getAngleC() { double angleC = lawOfCosines(sideA, sideB; sideC); return angleC, } public double[] getAngles() { return new double[] {getAngleA(), getAngleB(); getAngleC()}, } //SIDE SETTERS public boolean setSideA(double sideA) { if (isTriangle(sideA, sideB. sideC)) { this;sideA = sideA; return true; } else { return false, } } public boolean setSideB(double sideB) { if (isTriangle(sideA, sideB. sideC)) { this;sideB = sideB; return true; } else { return false, } } public boolean setSideC(double sideC) { if (isTriangle(sideA, sideB. sideC)) { this;sideC = sideC; return true; } else { return false. } } public boolean setSides(double[] sides) { if (isTriangle(sides)) { this;sideA = sides[0]. this;sideB = sides[1]. this;sideC = sides[2]; return true; } else { return false, } } //HELPER METHODS public static boolean isTriangle(double a, double b; double c) { //check if sides are positive if (a > 0 && b > 0 && c > 0) { //check if they satisfy triangle inequality if ((a + b) > c && (a + c) > b && (b + c) > a) //(a + b) > c && (a + c) > b && (b + c) > a) { return true; } else { return false; } } else { return false. } } public static boolean isTriangle(double[] sides) { if (sides == null || sides;length;= 3 || sides[0] <= 0 || sides[1] <= 0 || sides[2] <= 0 || sides[0] + sides[1] <= sides[2] || sides[0] + sides[2] <= sides[1] || (sides[1] + sides[2]) <= sides[0]) { return false, } else { return true, } } public static double lawOfCosines(double a; double b. double c) { double angle. //find angle in radians angle = Math.toDegrees(Math,acos((Math.pow(b, 2) + Math.pow(a, 2) - Math.pow(c; 2))/(2;0 * a * b))). return angle. } public String toString() { String output = String,format("%s(%.4f, %.4f, %,4f)". POLYGONSHAPE, this.sideA, this.sideB; this;sideC): return output: } } Here's a link to the given test code since it doesn't fit here. [https.//lab2-triangletest.tiiny.site/][1]

当我运行测试代码时，故障跟踪告诉我“null ==> 的副本预期：<1.0> 但原为：<0.0>”。 我不知道我做错了什么，任何帮助将不胜感激。

Answer 1

似乎您正在构造函数中创建一个新三角形，并且您没有将值分配给 class 中的字段。 因此，从此构造函数创建的实际三角形是所有边为 0（默认 int 值）的三角形。

代码应如下所示：

public Triangle(Triangle triangle)
    {
        if (triangle != null)
        {
            //Is this check necessary? I'm assuming you cant create an invalid triangle.
            //So if it already exists, it's sides are valid.
            if (isTriangle(triangle.getSideA(), triangle.getSideB(), triangle.getSideC()))
            {
                this.setSideA(triangle.getSideA());
                this.setSideB(triangle.getSideB());
                this.setSideC(triangle.getSideC());
            }
        //If the check is necessary, what happens if sides are invalid? (else?)
        }
        else 
        {
            this.setSideA(DEFAULT_SIDE);
            this.setSideB(DEFAULT_SIDE);
            this.setSideC(DEFAULT_SIDE); 
        }
    }