Collections工具类
Java里关于聚合的工具类，包含有各种有关集合操作的静态多态方法，不能实例化(把构造函数私有化)
public class Collections {
// Suppresses default constructor, ensuring non-instantiability.
private Collections() {
}
}
和Collection的区别
常见方法
排序
Sort(List list)
按自然排序的升序排序
public static void main(String[] args) {
List<String> list = new ArrayList<>();
list.add("aaaa");
list.add("zzz");
list.add("gggg");
System.out.println(list);
Collections.sort(list);
System.out.println(list);
}
自定义排序规则
Sort(List list,Comparator c)，由Comparator控制排序逻辑
public static void main(String[] args) {
List<String> list = new ArrayList<>();
list.add("aaaa");
list.add("zzz");
list.add("gggg");
System.out.println(list);
//默认升序
Collections.sort(list, Comparator.naturalOrder());
System.out.println(list);
//降序
Collections.sort(list, Comparator.reverseOrder());
System.out.println(list);
}
随机排序
shuffle(List list)
public static void main(String[] args) {
List<String> list = new ArrayList<>();
list.add("1");
list.add("2");
list.add("3");
list.add("4");
list.add("5");
list.add("6");
list.add("7");
list.add("8");
list.add("9");
list.add("10");
list.add("J");
list.add("Q");
list.add("K");
System.out.println(list);
Collections.shuffle(list);
System.out.println(list);
}
获取最值元素
max(Collection coll)#
默认比较，不适合对象比较
max(Collection coll,Comparator comparator)#
Student.java
package com.cyb.test;
class Student {
public Student(String name, int age) {
this.name = name;
this.age = age;
}
private int age;
private String name;
public void setAge(int age) {
this.age = age;
}
public int getAge() {
return age;
}
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
@Override
public String toString() {
return "Student{" + "age=" + age + ", name='" + name + '\'' + '}';
}
}
Test03.java
package com.cyb.test;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class test03 {
public static void main(String[] args) {
List<Student> list = new ArrayList<>();
list.add(new Student("jack", 26));
list.add(new Student("tom", 29));
list.add(new Student("mary", 32));
list.add(new Student("tony", 19));
list.add(new Student("smith", 41));
System.out.println(list);
Student maxAgeStudent = Collections.max(list, new Comparator<Student>() {
@Override
public int compare(Student o1, Student o2) {
return o1.getAge() - o2.getAge();
}
});
System.out.println("maxAgeStudent = "+maxAgeStudent.toString());
Student mixAgeStudent = Collections.min(list, new Comparator<Student>() {
@Override
public int compare(Student o1, Student o2) {
return o1.getAge() - o2.getAge();
}
});
System.out.println("mixAgeStudent = "+mixAgeStudent.toString());
}
}
创建不可变集合unmodifiablleXXX()
List<String> list = new ArrayList<>();
list.add("SpringBoot课程");
list.add("架构课程");
list.add("微服务SpringCloud课程"); //设置为只读List集合
list = Collections.unmodifiableList(list);
System.out.println(list);
Set<String> set = new HashSet<>();
set.add("Mysql教程");
set.add("Linux服务器器教程");
set.add("Git教程");
//设置为只读Set集合
set = Collections.unmodifiableSet(set);
System.out.println(set);
Map<String, String> map = new HashMap<>();
map.put("key1", "课程1");
map.put("key2", "课程2");
//设置为只读Map集合
map = Collections.unmodifiableMap(map);
System.out.println(map);
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。
