容器集合整理

package test2;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;

/**
 * 迭代器
 * 
 * @author Administrator
 */
public class Test4 {
    public static void main(String[] args) {

        List<String> list = new ArrayList<>();
        list.add("qqqq");
        list.add("wwww");
        list.add("eeee");
        
        Iterator<String> iter = list.iterator();
        
        while(iter.hasNext()) {
            String s = iter.next();
            System.out.println(s);
            if (s.equals("wwww")) {
                // iter.remove();
                list.remove(iter.next()); //尽量不要调用两次iter.next
            }
        }
        
        System.out.println(list);
        
        ListIterator<String> ls = list.listIterator();
        while(ls.hasPrevious()) {
            System.out.println(ls.previous());
        }
        /*
         * 需要注意的问题:
         *         迭代器中的remove方法, 绝对不可以与list中的remove(Object)方法混用
         *         会抛出ConcurrentModificationException这个异常
         *         next方法的调用
         */
    }
}

package test2;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class Test3 {

    public static void main(String[] args) {
        String[] arrs = {"aa","bb","cc","dd","aa","cc","ee","ee","cc","aa"}; //　　查询数组内字母出现了几次
        List<String> list = new ArrayList<>();
        list.add("qqqq");list.add("wwww");list.add("eeee");
        Set<String> set = new HashSet<>();
        set.add("1111");set.add("22222222222");set.add("3333333");
        
        for(String s1 : arrs) {
            System.out.println(s1);
        }
        for (String s2 : list) {
            System.out.println(s2);
        }
        for (String s3 : set) {
            System.out.println(s3);
        }
        
/*        Map<String, Integer> map = new HashMap<>();
        
        for (int i = 0; i < arrs.length; i++) {
            // map.put(arrs[i], map.get(arrs[i]) == null ? 1 : map.get(arrs[i]) + 1);
            Integer count = map.get(arrs[i]);
            if (count == null) {
                map.put(arrs[i], 1);
            } else {
                map.put(arrs[i], count + 1);
            }
        }
        System.out.println(map);*/
    }

}