在 ArrayDeque containsAll(Collection c)、contains(Object o)、equals(Object o) 中给出预期但 equals(Collection c) 给出意外结果

Question

我有以下“人物”class -

import java.util.Objects;

public class Person implements Comparable<Person> {
    private int id;
    private String name;

    Person(int id, String name) {
        this.id = id;
        this.name = name;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }


    @Override
    public int compareTo(Person person) {
        int myReturn = 0;
        int minLength = 0;
        boolean equal = false;
        int id1 = id;
        int id2 = person.id;
        String name1 = name;
        String name2 = person.name;

        if (name1.length() > name2.length()) {
            minLength = name2.length();
        } else if (name1.length() < name2.length()) {
            minLength = name1.length();
        } else {
            minLength = name1.length();
            equal = true;
        }

        if (id1 > id2) {
            myReturn = 1;
        } else if (id1 < id2) {
            myReturn = -1;
        } else {
            int i = 0;
            for (i = 0; i < minLength; i++) {
                if (name1.charAt(i) > name2.charAt(i)) {
                    myReturn = 1;
                    break;
                } else if (name1.charAt(i) < name2.charAt(i)) {
                    myReturn = -1;
                    break;
                } else {
                    continue;
                }
            }
            if(i == minLength) {
                if (equal) {
                    myReturn = 0;
                } else if (name1.length() > minLength) {
                    myReturn = 1;
                } else {
                    myReturn = -1;
                }
            }
        }
        return myReturn;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        Person person = (Person) obj;
        return id == person.id && Objects.equals(name, person.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, name);
    }
}

现在以下代码的行为符合预期 -

代码 1：

/* equals(Object object) - method */
        Person person3 = new Person(2, "Neha");
        Person person4 = new Person(2, "Neha");
        Person person5 = new Person(2, "Sneha");
        System.out.println(person3.equals(person4));
        System.out.println(person3.equals(person5));

输出-

true
false

代码 2：

/* contains(Object object) - method */
        ArrayDeque<Person> arrayDeque13 = new ArrayDeque<>(List.of(
                new Person(99, "Needhi"),
                new Person(12, "Papori"),
                new Person(78, "Pallavi")
        ));
        Person person1 = new Person(12, "Papori");
        Person person2 = new Person(13, "Puja");
        System.out.println(arrayDeque13.contains(person1));
        System.out.println(arrayDeque13.contains(person2));

输出-

true
false

代码 3：

/* containsAll(Collection collection) - method */
        ArrayDeque<Person> arrayDeque14 = new ArrayDeque<>(List.of(
                new Person(3, "Namita"),
                new Person(2, "Mridu"),
                new Person(82, "Priyadarshini"),
                new Person(89, "Tina"),
                new Person(13, "Kajal")
        ));
        ArrayDeque<Person> arrayDeque15 = new ArrayDeque<>(List.of(
                new Person(3, "Namita"),
                new Person(2, "Mridu"),
                new Person(13, "Kajal")
        ));
        ArrayDeque<Person> arrayDeque16 = new ArrayDeque<>(List.of(
                new Person(3, "Namita"),
                new Person(2, "Mridu"),
                new Person(13, "Neha")
        ));
        System.out.println(arrayDeque14.containsAll(arrayDeque15));
        System.out.println(arrayDeque14.containsAll(arrayDeque16));

输出-

true
false

但是下面的代码没有按预期运行 -

代码 4：

/* equals(Collection collection) - method */
        ArrayDeque<Person> arrayDeque17 = new ArrayDeque<>(List.of(
                new Person(56, "Leena"),
                new Person(66, "Nidhi"),
                new Person(76, "Payal")
        ));
        ArrayDeque<Person> arrayDeque18 = new ArrayDeque<>(List.of(
                new Person(56, "Leena"),
                new Person(66, "Nidhi"),
                new Person(76, "Payal")
        ));
        ArrayDeque<Person> arrayDeque19 = new ArrayDeque<>(List.of(
                new Person(56, "Leena"),
                new Person(66, "Nidhi"),
                new Person(76, "Payel")
        ));
        System.out.println(arrayDeque17.equals(arrayDeque18));
        System.out.println(arrayDeque17.equals(arrayDeque19));

输出-

false
false

在这里，我希望第一个输出是 true 但它是 false

如 -

https://docs.oracle.com/javase/7/docs/api/java/util/ArrayDeque.html

Methods inherited from interface java.util.Collection
addAll, containsAll, equals, hashCode, removeAll, retainAll

那么，我哪里错了？

Answer 1

正如评论者已经提到的，ArrayDeque 没有实现 equals()。如果不确定，请查看 javadoc 并搜索“等于”。如果它在“从 class java.lang.Object 继承的方法”下，那么您知道它正在使用 Object 的 equals 实现：

接口不能有equals()方法实现，因为Java不允许default等值方法。如果 class 实现了多个接口，每个接口都包含一个默认的“equals”方法，应该使用哪一个？所以它是从 Collection 接口继承的有点无关紧要。 Javadoc 在那里列出它是因为 Collection 接口明确定义了 equals() 和 collection-specific javadoc。

在 ArrayDeque containsAll(Collection c)、contains(Object o)、equals(Object o) 中给出预期但 equals(Collection c) 给出意外结果

In ArrayDeque containsAll(Collection c), contains(Object o), equals(Object o) give expected but equals(Collection c) gives unexpected result

java

collections

overriding

equals

arraydeque