十五、Collections.sort(<T>, new Comparator<T>() {})针对字符串排序

1、排序对象全是字母组成，可以根据ASCII编码表排序

package com.abcd;

public class Person{

    private String name;
    private int age;
    private int salary;

    public Person() {
    }

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

    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;
    }

    public int getSalary() {
        return salary;
    }

    public void setSalary(int salary) {
        this.salary = salary;
    }

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

}

2、排序测试代码

package com.abcd;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class PersonTest {
    public static void main(String[] args){
        List<Person> people = new ArrayList<>();
        people.add(new Person("ZZZ",20,100));
        people.add(new Person("aaa",48,109));
        people.add(new Person("aa",30,109));

        System.out.println(people);
        Collections.sort(people, new Comparator<Person>() {
            @Override
            public int compare(Person o1, Person o2) {

                return o1.getName().toLowerCase().compareTo(o2.getName().toLowerCase());

            }
        });
        System.out.println(people);
    }
}

int comparaTo( )方法底层源码：

public int compareTo(String anotherString) {
        int len1 = value.length;
        int len2 = anotherString.value.length;
        int lim = Math.min(len1, len2);
        char v1[] = value;
        char v2[] = anotherString.value;

　　　　　//首先的比较规则，比较首字母，依次第二位字母，第三位字母等逐个比较
        int k = 0;
        while (k < lim) {
            char c1 = v1[k];
            char c2 = v2[k];
            if (c1 != c2) {
                return c1 - c2;
            }
            k++;
        }
　　　　　//然后字母比较完了后，比较字符串的长度
        return len1 - len2;
    }

3、运行结果

[Person{name='ZZZ', age=20, salary=100}, Person{name='aaa', age=48, salary=109}, Person{name='aa', age=30, salary=109}]
[Person{name='aa', age=30, salary=109}, Person{name='aaa', age=48, salary=109}, Person{name='ZZZ', age=20, salary=100}]

---

2、排序目标全是中文，实现首字母排序

package com.abcd;

import java.text.Collator;
import java.util.*;

public class PersonTest {
    public static void main(String[] args){
        List<Person> people = new ArrayList<>();
        people.add(new Person("博泰",20,100));
        people.add(new Person("阿明",48,109));
        people.add(new Person("啊",30,109));

        System.out.println(people);
        Collections.sort(people, new Comparator<Person>() {
            @Override
            public int compare(Person o1, Person o2) {

                Comparator cmp = (Collator.getInstance(Locale.CHINA));
                return cmp.compare(o1.getName(), o2.getName());

            }
        });
        System.out.println(people);
    }
}

运行结果：

[Person{name='博泰', age=20, salary=100}, Person{name='阿明', age=48, salary=109}, Person{name='啊', age=30, salary=109}]
[Person{name='啊', age=30, salary=109}, Person{name='阿明', age=48, salary=109}, Person{name='博泰', age=20, salary=100}]