物件比較器

對兩個或多個數據項進行比較, 以確定它們是否相等, 或確定它們之間的大小關係及排序順序稱為比較.

1、Arrays.sort()方法可以實現物件的排序操作

public static void sort(Object[] a)

程式碼實現:

int[] nums = {34,56,28,37,98,16};
Arrays.sort(nums);
System.out.println(Arrays.toString(nums));
String[] names = {"lucy","jack","lili","tom"};
Arrays.sort(names);
System.out.println(Arrays.toString(names));
 

執行結果:

2、Comparable介面

此介面強行對實現它的每個類的物件進行整體排序. 這種排序被稱為類的自然排序, 類的compareTo方法稱為它的自然比較方法.

程式碼實現:

//自定義物件,要實現比較排序: 可以實現Comparable<T>的compareTo方法
Cat[] cats = {new Cat("笨笨",1),
new Cat("菲菲",8),
new Cat("笑笑",6)};
Arrays.sort(cats);
System.out.println(Arrays.toString(cats));

package cesi.tomcat.entity;

/**
 * Created by gailun on 2018/11/3.
 */
public class Cat implements Comparable<Cat>{
    private String name;
    private Integer age;

    public Cat() {
    }

    public Cat(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

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

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

    @Override
    public int compareTo(Cat o) {
        if (this.age<o.age) return -1;
        if (this.age>o.age) return 1;
        return 0;
    }
}
 

執行結果:

3、Comparator介面

Comparator介面是要求自定義類去實現, 按照oo原則; 強行對某個物件collection進行整體排序的比較.

程式碼實現:

Person[] persons = {new Person("笨笨",1),
        new Person("菲菲",8),
        new Person("笑笑",6)};
Arrays.sort(persons, new Comparator<Person>() {
    @Override
    public int compare(Person o1, Person o2) {
        return o1.getAge()-o2.getAge();
    }
});
System.out.println(Arrays.toString(persons));
 

package cesi.tomcat.entity;
/**
 * Created by gailun on 2018/11/3.
 */
public class Person {
    private String name;
    private Integer age;

    public Person() {
    }

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

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

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

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

執行結果: