Collection集合的常用方法和遍历

练习程序

package _4;

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

//Collection集合常用方法
//boolean add(E e)添加
//boolean remove(Object o)移除
//void clear()清空
//boolean contains(Object 0)判断元素是否存在
//boolean isEmpty()判断是否为空
//int size()元素个数
public class _222 {
    public static void main(String[] args) {

        Collection c = new ArrayList();


        //boolean add(E e)添加
        System.out.println(c.add("hello"));
        System.out.println(c.add("world"));
        System.out.println(c.add("world"));


        //boolean remove(Object o)移除
        System.out.println(c.remove("world"));
        System.out.println(c.remove("qweer"));


        //void clear()清空
 //     c.clear();


        //boolean contains(Object 0)判断元素是否存在
        System.out.println(c.contains("world"));
        System.out.println(c.contains("sdrev"));

        //boolean isEmpty()判断是否为空
        System.out.println(c.isEmpty());

        //int size()元素个数
        System.out.println(c.size());




        //输出集合
        System.out.println(c);




    }

}

 遍历

练习程序

package _4;

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

//Collection遍历
public class _223 {
    public static void main(String[] args) {
        Collection c = new ArrayList();
        c.add("hello");
        c.add("world");
        c.add("java");

        Iterator it = c.iterator();
        
        //E next()返回迭代中的下一个元素
        


        //boolean hasNext()如果迭代具有更多元素,则返回true
        


        //用while改进
        while (it.hasNext()){
            //System.out.println(it.next());
            String s=it.next();
            System.out.println(s);
        }



    }
}