collection集合和源码

collection集合和源码 集合 collection集合 map list集合三种循环

 List list = new ArrayList<>();
        list.add("1");
        list.add("2");
        list.add("3");
        //1.常用的循环
        for (int i = 0; i < list.size(); i++) {
            String o = list.get(i);
            System.out.println(o);
        }
        System.out.println("=====================");
        //2.增强for
        for (String s : list) {
            System.out.println(s);
        }
        System.out.println("=====================");
        //3.迭代器删除，会把本次的结果删除，下次使用的时候结果为空
        Iterator iterator = list.iterator();
        while ( iterator.hasNext() ) {
            String next = iterator.next();
            iterator.remove();
            System.out.println(next);
        }
        System.out.println(list.size());
        System.out.println("=====================删除后测试遍历，结果为空");
        for (String s : list) {
            System.out.println(s);
        }
        //总结：增强for环境的本地就是迭代器，会编译成迭代器，可以查询编译后的代码
        // Iterator iterator = list.iterator();
        //
        // while(iterator.hasNext()) {
        //     next = (String)iterator.next();
        //     System.out.println(next);
        // }
        //
        // System.out.println("=====================");
        // iterator = list.iterator();
        //
        // while(iterator.hasNext()) {
        //     next = (String)iterator.next();
        //     System.out.println(next);
        // }

练习list排序

public static void main(String[] args) {
        List