Java自然排序與定製排序

一、自然排序

自然排序：類實現了java.lang.Comparable接口，重寫compareTo()的規則

如果當前對象this大於形參對象obj，則返回正整數；如果當前對象this小於形參對象obj，則返回負整數；如果當前對象this等於參數對象obj，則返回零。

1.Person類

public class Person implements Comparable<Person> {
    private Integer age;

    public Person(Integer age) {
        this.age = age;
    }

    @Override
    public int compareTo(Person person) {
        return this.age - person.age;
    }

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

2.測試

Arrays有方法public static void sort(Object[] a)

@Test
public void test1() {
    Person[] peoples = new Person[4];
    peoples[0] = new Person(11);
    peoples[1] = new Person(19);
    peoples[2] = new Person(18);
    peoples[3] = new Person(10);

    Arrays.sort(peoples);

    System.out.println(Arrays.toString(peoples));
}

3.結果

二、定製排序

定製排序：java.util.Comparator

當元素的類型沒有實現java.lang.Comparable接口而又不方便修改代碼時，那麼可以考慮使用Comparator的對象來排序

1.Person類

public class Person {
    private Integer age;

    public Person(Integer age) {
        this.age = age;
    }

    public Integer getAge() {
        return age;
    }

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

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

2.測試

Arrays有方法public static <T> void sort(T[] a, Comparator<? super T> c)

@Test
public void test2() {
    Person[] peoples = new Person[4];
    peoples[0] = new Person( 13);
    peoples[1] = new Person(19);
    peoples[2] = new Person(17);
    peoples[3] = new Person(16);

    Arrays.sort(peoples, new Comparator<Person>() {
        @Override
        public int compare(Person person1, Person person2) {
            return person1.getAge() - person2.getAge();
        }
    });

    System.out.println(Arrays.toString(peoples));
}

3.結果