零基础java自学流程-Java语言进阶128

定制排序（在集合中写排序规则）

TreeSet还有一种排序就是定制排序，定制排序时候，需要关联一个Comparator对象，由Comparator提供排序逻辑。下面就是一个使用Lambda表达式代替Comparator对象来提供定制排序的例子。下面是一个定制排序的列子

import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;


public class TestSets {
    public static void main(String[] args) {
        Set set = new TreeSet(new MyCommpare());
        set.add(new M(5));
        set.add(new M(3));
        set.add(new M(9));
        System.out.println(set);
    }
    
}

class M {
    int age;

    public M(int age) {
        this.age = age;
    }
}

class MyCommpare implements Comparator {
    @Override
    public int compare(Object o1, Object o2) {
        M m1 = (M) o1;
        M m2 = (M) o2;
        return m1.age > m2.age ? 1 : m1.age < m2.age ? -1 : 0;
    }
}

当然将Comparator直接写入TreeSet初始化中也可以。如下。

import org.junit.Test;

import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;


public class TestSets {
    public static void main(String[] args) {
        Set set = new TreeSet(new MyCommpare());
        set.add(new M(5));
        set.add(new M(3));
        set.add(new M(9));
        System.out.println(set);
    }

    
    @Test
    public void testTreeSet() {
        Set set = new TreeSet(new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                M m1 = (M) o1;
                M m2 = (M) o2;
                return m1.age > m2.age ? 1 : m1.age < m2.age ? -1 : 0;
            }
        });
        set.add(new M(5));
        set.add(new M(3));
        set.add(new M(9));
        System.out.println(set);
    }

    
    @Test
    public void testTreeSetLam() {
        Set set = new TreeSet((o1, o2) -> {
            M m1 = (M) o1;
            M m2 = (M) o2;
            return m1.age > m2.age ? 1 : m1.age < m2.age ? -1 : 0;
        });
        set.add(new M(5));
        set.add(new M(3));
        set.add(new M(9));
        System.out.println(set);
    }

}

class M {
    int age;

    public M(int age) {
        this.age = age;
    }
}

class MyCommpare implements Comparator {
    @Override
    public int compare(Object o1, Object o2) {
        M m1 = (M) o1;
        M m2 = (M) o2;
        return m1.age > m2.age ? 1 : m1.age < m2.age ? -1 : 0;
    }
}

class Err implements Comparable {
    @Override
    public int compareTo(Object o) {
        return 0;
    }