Java比较器

Java比较器分内外部比较器（Comparable、Comparator），

Comparable 是在集合内部定义的方法实现的排序，Comparator 是在集合外部实现的排序。

想实现排序，就需要在集合内实现 Comparable 接口的方法 或者 在集合外定义 Comparator 接口的方法。

Comparable位于包java.lang，Comparator位于包java.util下

Comparable接口声明了compareTo(Object o)方法，Comparator 接口声明了compare(Object o1,Object o2)方法

代码来自于https://blog.youkuaiyun.com/xian_canhui/article/details/70230975

内部，实现较麻烦。

public class Test {
    public static void main(String[] args) {
        //创建TreeSet并加入worker对象
        TreeSet<Worker> set = new TreeSet<Worker>();
        set.add(new Worker("zhang3", 18));
        set.add(new Worker("li4", 25));
        set.add(new Worker("wang5", 22));
        set.add(new Worker("lao6", 22));
        set.add(new Worker("xiaoming", 22));

        //遍历输出信息
        Iterator<Worker> iterator = set.iterator();
        while (iterator.hasNext()) {
            Worker worker = iterator.next();
            System.out.println(worker);
        }
    }
}

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

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

    /*
     * 先按年龄排，次要按名字排
     * 负整数、零或正整数，根据此对象是小于、等于还是大于指定对象。
     */
    @Override
    public int compareTo(Worker w) {
        int sub = this.age - w.age;
        if (sub == 0)
            return this.name.compareTo(w.name);//使用String的comareTo方法
        else
            return sub;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    @Override
    public String toString() {
        return "Worker [name=" + name + ", age=" + age + "]";
    }

}

内部

public class Test {
    public static void main(String[] args) {
        //创建List并加入worker对象
        List<Worker> list = new ArrayList<Worker>();
        list.add(new Worker("zhang3", 18));
        list.add(new Worker("li4", 25));
        list.add(new Worker("wang5", 22));
        list.add(new Worker("lao6", 22));
        list.add(new Worker("xiaoming", 22));

        Collections.sort(list, new MyComparator());//传入list和比较器排序

        //遍历输出信息
        for (int i = 0; i < list.size(); i++) {
            Worker worker = list.get(i);
            System.out.println(worker);
        }
    }
}

public class Worker {
    private String name;
    private int age;

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    @Override
    public String toString() {
        return "Worker [name=" + name + ", age=" + age + "]";
    }

}

public class MyComparator implements Comparator<Worker> {
    /*
     * 先按年龄排，次要按名字排
     * 根据第一个参数小于、等于或大于第二个参数分别返回负整数、零或正整数
     */
    @Override
    public int compare(Worker o1, Worker o2) {
        int sub = o1.getAge() - o2.getAge();
        if (sub == 0)
            return o1.getName().compareTo(o2.getName());//使用String的comareTo方法
        else
            return sub;
    }

}