Java（22）：集合

集合：可以存储不同类型的对象（一般是同类型），可以增删，相比数组更加灵活

import java.util.ArrayList;
import java.util.Collection;

public class CollectionDemo {

    public static void main(String[] args) {
    
        Collection c1 = new ArrayList();
        c1.add("abc1");
        c1.add("abc2");
        c1.add("abc3");
        c1.add("abc4");    
        System.out.println(c1);
//        .clear()方法移除所有元素
        c1.clear();
        System.out.println(c1);
        
        Collection c2 = new ArrayList();
        c2.add("abc5");
        c2.add("abc6");
        c2.add("abc7");
        c2.add("abc8");
//        .remove()方法移除某一个元素，返回boolean值
        System.out.println(c2.remove("abc6")); // true
        System.out.println(c2);
//        .size()方法返回元素个数
        System.out.println(c2.size());
        
    }
}

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class CollectionDemo1 {

    public static void main(String[] args) {
        
        Collection c = new ArrayList();
        c.add("hello");
        c.add("world");
        c.add("java");
        c.add("hi");
        System.out.println(c);
        
//        集合转为数组，遍历
        Object[] objs = c.toArray();
        for (int i=0; i<objs.length; i++) {
            System.out.print(objs[i]);
            String str = (String) objs[i];
            System.out.println(", "+ str.length());
        }
        
//        迭代器遍历
        Iterator it = c.iterator();
//        .hasNext()方法判断是否存在下一个元素
        while(it.hasNext()) {
            String s = (String) it.next();
            System.out.print(s+", ");
        }
        
    }
    
}

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class CollectionDemo2 {

    public static void main(String[] args) {
        
        Collection c = new ArrayList();
        
        Person p1 = new Person("貂蝉", 10);
        Person p2 = new Person("吕布", 25);
        Person p3 = new Person("孙权", 22);
//        对象添加到集合
        c.add(p1);
        c.add(p2);
        c.add(p3);
        
        Object[] obj = c.toArray();
        for(int i=0; i<obj.length; i++) {
            Person p = (Person) obj[i];
            System.out.println(p.getName() + ": " + p.getAge());
        }
        
        System.out.println("******");
        
        c.add(new Person("诸葛亮", 18));
        
        Iterator iterator = c.iterator();
        while (iterator.hasNext()) {
            Person p = (Person) iterator.next();
            System.out.println(p.getName() + ": " + p.getAge());
        }
        
    }
    
}

class Person {
    private String name;
    private int age;
    
    public Person() {
        super();
    }
    public Person(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    
    public String getName() {
        return this.name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return this.age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}

参考博客：https://www.cnblogs.com/lyywj170403/p/9378881.html