英文:
Why is the test failing when comparing two of the same objects in Java?
问题
我正在尝试制作一个多项式计算器，以学习编程。在我进行测试时，有一个部分在比较两个相同的对象时失败了，这对我来说毫无意义。请看下面的测试单元，它正在失败。
@Test
public void testAddition() {
P1 = new PolynomialImp("12x^2+5");
P2 = new PolynomialImp("16x^2+6");
Polynomial P3 = P1.add(P2);
Polynomial P4 = new PolynomialImp("28x^3+11");
assertTrue(P3.equals(P4));
}
问题是，即使我将测试者更改为以下内容，它仍然失败。
@Test
public void testAddition() {
P1 = new PolynomialImp("12x^3+5");
P2 = new PolynomialImp("16x^3+6");
Polynomial P3 = new PolynomialImp("28x^3+11");
Polynomial P4 = new PolynomialImp("28x^3+11");
assertTrue(P3.equals(P4));
}
考虑到它们都是用相同的变量创建的，它不应该通过吗？
英文:
I'm trying to make a polynomial calculator to learn how to code and as I'm testing it there's a part which fails when comparing two of the same objects which is not making any sense to me. See the following test unit that is failing.
@Test
public void testAddition() {
P1 = new PolynomialImp("12x^2+5");
P2 = new PolynomialImp("16x^2+6");
Polynomial P3 = P1.add(P2);
Polynomial P4 = new PolynomialImp("28x^3+11");
assertTrue(P3.equals(P4));
}
The thing is, it fails even when I change the tester to the following.
@Test
public void testAddition() {
P1 = new PolynomialImp("12x^3+5");
P2 = new PolynomialImp("16x^3+6");
Polynomial P3 = new PolynomialImp("28x^3+11");
Polynomial P4 = new PolynomialImp("28x^3+11");
assertTrue(P3.equals(P4));
}
Shouldn't it pass considering they are both created with the same variables?
答案1
得分: 0
P3.equals(P4)检查P3和P4是否为同一个对象的实例。您需要重写equals方法并相应地返回true或false。
英文:
P3.equals(P4) checks whether P3 and P4 are the same instance of an object. You have to override the equals method to return true or false accordingly.
答案2
得分: 0
equals() 的默认实现仅在两个对象为同一对象时返回 true，因此仅在 P3.equals(P3) 的情况下返回 true，或者如果您执行以下操作：
P3 = new ...
P4 = P3;
P3.equals(P4); // true
如果您需要基于程序逻辑的等同性（即，如果两个多项式使用相同的字符串进行初始化，则它们相等），您必须重写您的类的 equals() 方法并自行实现该逻辑。
英文:
The default implementation of equals() is only true when both objects are the same object, so only for P3.equals(P3) or if you do
P3 = new ...
P4 = P3;
P3.equals(P4); // true
If you need equivality based on the logic of your program (i.e. 2 polynomials are equal if they are initialized with the same string), you have to override the equals() methof of your class and implement that logic yourself.
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