Java 比较器 -- 对象比较

基本数据类型比较大小时，我们可以用比较运算符。当两个对象比较大小时，我们就可以用比较器了。实现的方式有两种，如下：

方式一：自然排序，实现接口Comparable

创建一个自定义类Students，实现接口Comparable，并重写compareTo方法，在方法体中规定排序规则。

class Students implements Comparable{
    private String name;
    private int age;

    public Students() {
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

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

    @Override
    public int compareTo(Object o) {
        if(o instanceof Students){
            Students obj = (Students) o;

            /**
             * 当前对象属性大于参数的对象属性，返回值为正数时是从小到大排序
             * 当前对象属性小于参数的对象属性，返回值为正数时是从大到小排序
             */
            if(this.getAge() > obj.getAge()){
                return 1;
            }else if (this.getAge() < obj.getAge()){
                return -1;
            }else{
                return this.getName().compareTo(obj.getName());
            }
        }
        throw new RuntimeException("参数类型错误");
    }
}

public class CompareTest{
    public static void main(String[] args) {
        Students[] students = new Students[]{
                new Students("李雷", 26),
                new Students("黎明", 24),
                new Students("王伟", 29),
                new Students("艾米", 26),
        };

        Arrays.sort(students);

        System.out.println(Arrays.toString(students));
        // [Students{name='黎明', age=24}, Students{name='李雷', age=26}, Students{name='艾米', age=26}, Students{name='王伟', age=29}]
    }
}

方式二：定制排序，不需要实现接口Comparable

class Students{
    private String name;
    private int age;

    public Students() {
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

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

public class CompareTest{
    public static void main(String[] args) {
        Students[] students = new Students[]{
                new Students("李雷", 26),
                new Students("黎明", 24),
                new Students("王伟", 29),
                new Students("艾米", 26),
        };

        Arrays.sort(students, new Comparator<Students>() {
            @Override
            public int compare(Students o1, Students o2) {
                /**
                 * 当前对象属性大于参数的对象属性，返回值为正数时是从小到大排序
                 * 当前对象属性小于参数的对象属性，返回值为正数时是从大到小排序
                 */
                if(o1.getAge() > o2.getAge()){
                    return 1;
                }else if (o1.getAge() < o2.getAge()){
                    return -1;
                }else{
                    return o1.getName().compareTo(o2.getName());
                }
            }
        });
        
        System.out.println(Arrays.toString(students)); // [Students{name='黎明', age=24}, Students{name='李雷', age=26}, Students{name='艾米', age=26}, Students{name='王伟', age=29}]
    }
}