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
Collection是接口，提供了对集合对象进行基本操作的通用接口方法，List、Set等多种具体的实现类
Collection是工具类，专门从操作Collection接口实现类里面的元素
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 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 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 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.javapackage 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.javapackage 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 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() {@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() {@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 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 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 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。
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