Java中对象的比较

一，基本数据类型的比较

二，引用数据类型比较

1，equals()方法

class Student {
    public String name;
    public int age;

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

public class Test {
    public static void main(String[] args) {
        Student student1 = new Student("张三", 19);
        Student student2 = new Student("张三", 19);
        System.out.println(student1.equals(student2));//输出false
    }

这里的输出结果任然是个false，是因为在Student类中我们没有equals方法，他默认调用的是object当中的equals方法，这里要自己实现一个equals来进行比较，在Generate中找到equals()和hashCode()点击，生成一下代码段：

 @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return age == student.age && Objects.equals(name, student.name);
    }

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

这样就可以输出一个true了；但是equals只能比较俩个对象是否相同，并不能比较俩个对象的大小，如果要比较对象的大小，有俩种方法可以去搞：

1）实现Comparable接口

//实现接口去比较对象的大小
class Student implements Comparable<Student>{
    public String name;
    public int age;

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return age == student.age && Objects.equals(name, student.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }
//重写compareTo的方法，用于比较对象的年龄
    @Override
    public int compareTo(Student o) {
        return this.age - o.age;
    }
}

public class Test {
    public static void main(String[] args) {
        Student student1 = new Student("张三", 19);
        Student student2 = new Student("张三", 20);
        System.out.println(student1.equals(student2));
        System.out.println(student1.compareTo(student2));//输出-1
    }

2）传比较器

class Student implements Comparable<Student> {
    public String name;
    public int age;

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return age == student.age && Objects.equals(name, student.name);
    }

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

    @Override
    public int compareTo(Student o) {
        return this.age - o.age;
    }
}

//名字比较器
class NameComparator implements Comparator<Student> {
    @Override
    public int compare(Student o1, Student o2) {
        return o1.name.compareTo(o2.name);
    }
}

//年龄比较器
class AgeComparator implements Comparator<Student> {
    @Override
    public int compare(Student o1, Student o2) {
        return o1.age - o2.age;
    }
}

public class Test {
    public static void main(String[] args) {
        Student student1 = new Student("李四", 19);
        Student student2 = new Student("张三", 20);
        //System.out.println(student1.equals(student2));
        //System.out.println(student1.compareTo(student2));
        NameComparator nameComparator = new NameComparator();
        //比较要比较的参数，如果student1大于student2，返回一个正数，如果相等返回0，再者就返回一个负数
        System.out.println(nameComparator.compare(student1, student2));
        AgeComparator ageComparator = new AgeComparator();
        System.out.println(ageComparator.compare(student1, student2));

    }
}