java - 如何在java中使用Arrays.equals()比较对象数组？

Question

在此示例中展示了如何执行此操作:

Student[] stud1 = new Student[2];
Student[] stud2 = new Student[2];
Student[] stud3 = new Student[2];
boolean b;
stud1[0]= new Student("Johnny","Bravo");
stud1[1]= new Student("Ace","Ventura");
stud2[0]= new Student("Ash","Ketchum");
stud2[1]= new Student("Mike","Wazowski");
b = Arrays.equals(stud1,stud2);
System.out.println(b);
stud2 [0] = stud1[0];
stud2[1] = stud1[1];
b = Arrays.equals(stud1,stud2);
System.out.println(b); 
stud3 = stud1;
b = Arrays.equals(stud1,stud3);
System.out.println(b);
}

结果是假真真。 Arrays.equals 到底比较什么？ 谢谢。

Answer 1

直接来自the docs :

Returns true if the two specified arrays of Objects are equal to one another. The two arrays are considered equal if both arrays contain the same number of elements, and all corresponding pairs of elements in the two arrays are equal. Two objects e1 and e2 are considered equal if (e1==null ? e2==null : e1.equals(e2)). In other words, the two arrays are equal if they contain the same elements in the same order. Also, two array references are considered equal if both are null.

这几乎解释了一切。在您的情况下，第一个输出是 false因为stud1和stud2有 Student 的实例不相等。在第二种情况下，两个数组具有相同的对象，因此测试为相等。在第三种情况下，stud1和stud3是同一个对象，因此也相等。

唯一有趣的情况是 Student有一个equals()方法，并且您想要测试两个具有等效但不相同的数组 Student对象:

Student[] stud1 = {
    new Student("Johnny","Bravo")
};
Student[] stud2 = {
    new Student("Johnny","Bravo")
};
System.out.println(Arrays.equals(stud1, stud2));

此处的输出取决于 Student.equals() 的实现.