对象比较器

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对象比较器

1.先说Arrays.sort快排常见

比较数字从小到大

<span style="font-size:18px;">int[] nums = {12,32,44,5,4,65};Arrays.sort(nums);for (int i : nums){System.out.println(i);}</span>

sort也可以用来排列字符型数组（按字典序排序）

String[] names = {"abc","vince","java","com","tom"};Arrays.sort(names);for (String string : names){System.out.println(string);}

2.如果要用sort比较自己定义的类

比如用自己定义的类Cat Arrays.sort(Cat);报错！

产生错误的原因差api知

Comparable没有Cat自定义类实现

代码实现：

所以Cat函数要这样写用comparato函数比较大于返回1小于返回-1等于返回0；

<span style="font-size:18px;">package com.vince;public class Cat implements Comparable<Cat>{// 告诉其所要对比的对象private String name;private int age;//应用快捷键shift+Alt+s或 鼠标右键-->源码public Cat() {}public Cat(String name, int age) {super();this.name = name;this.age = age;}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;}@Overridepublic String toString() {return "Cat [name=" + name + ", age=" + age + "]";}<span style="color:#ff0000;">//通过此方法实现对象的比较@Overridepublic int compareTo(Cat o) {if(this.age<o.age){return -1;}else if (this.age>o.age){return 1;}else{return 0;}}</span>}</span>

然后可以直接使用Arrays.sort(Cat)排序

//类不能被sort的接收(Cat 不能转化为Comparable接口）Cat[] cats = {new Cat("Tom",2),new Cat("GG",4),new Cat("Wg",3),new Cat("Bi",8),new Cat("DD",5)};Arrays.sort(cats);for (Cat cat : cats) {System.out.println(cat);}

输出结果

自定义比较类型用comparator(比较器)

假如类已经定义好了，不能再去修改它：

<span style="font-size:18px;">package com.vince;public class Dog {private String name;private int age;public Dog(String name, int age) {super();this.name = name;this.age = age;}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;}@Overridepublic String toString() {return "Dog [name=" + name + ", age=" + age + "]";}}</span>

没有定义比较端口要实现类比较

Comparator可以比较灵活的比较对象中的属性

<span style="font-size:18px;">package com.vince;import java.util.Comparator;public class DogComparator implements Comparator<Dog>{@Overridepublic int compare(Dog o1, Dog o2) {if (o1.getAge()<o2.getAge()){return -1;}else if (o1.getAge()>o2.getAge()){return 1;}return 0;}</span>}

所以要用sort比较时要告诉sort函数比较器

<span style="font-size:18px;">//类不能被sort的接收(Dog 重新写comparator写比较的属性）Dog[] dogs = {new Dog("Tom",2),new Dog("GG",4),new Dog("Wg",3),new Dog("Bi",8),new Dog("DD",5)};Arrays.sort(dogs,new DogComparator());//比较类内的属性用重写DogComparablefor (Dog dog : dogs) {System.out.println(dog);}</span>

输出结果和Cat一样

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