增强for循环学习笔记

标签：增强for循环   for   java   

package com.lc.day01.ForEnhance;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import org.junit.Test;

public class forEnhance {

	@Test
	public void ArrayForEnhance() {

		int arr[] = { 1, 2, 3 };
		for (int num : arr) {
			System.out.println("num");
		}
	}

	@Test
	public void ListForEnhance() {
		List list = new ArrayList();
		list.add(1);
		list.add(2);
		list.add(3);
		list.add(4);

		for (Object obj : list) {
			int i = (Integer) obj;
			System.out.println(i);
		}

	}

	/*
	 * 1.HashMap()是根据算法存的 2.如果需要按顺序存储的话使用LinkedHashMap()
	 */
	@Test
	public void MapForEnhance() {
		// Map map = new HashMap(); //根据算法存的
		Map map = new LinkedHashMap(); // 按着自己存放的顺序 存储
		map.put("1", "aaa");
		map.put("2", "bbb");
		map.put("3", "ccc");
		map.put("4", "fff");
		map.put("5", "rrr");

		/*
		 * 1.传统方式1
		 */
		Set set = map.keySet();
		Iterator it = set.iterator();
		while (it.hasNext()) {
			String key = (String) it.next();
			String value = (String) map.get(key);
			System.out.println(key + "=" + value);
		}
		System.out.println("------------------------");
		/*
		 * 2.传统方式2
		 */
		Set set1 = map.entrySet();
		Iterator it1 = set1.iterator();
		while (it1.hasNext()) {
			Map.Entry entry = (Entry) it1.next();
			String key = (String) entry.getKey();
			String value = (String) entry.getValue();
			System.out.println(key + "=" + value);
		}
		System.out.println("------------------------");
		/*
		 * 3.利用增强for循环1
		 */
		for(Object obj:map.keySet()){
			String key = (String)obj;
			String value = (String)map.get(key);
			System.out.println(key + "=" + value);
		}
		
		System.out.println("------------------------");
		/*
		 * 4.利用增强for循环2
		 */
		for(Object obj:map.entrySet()){
			Map.Entry entry1 = (Entry)obj;
			String key = (String) entry1.getKey();
			String value = (String) entry1.getValue();
			System.out.println(key + "=" + value);
		}
		
	}
	
	@Test
	/*
	 * 使用增强for循环要注意的事情：增强for循环只适合取数据
	 */
	public void ForEnhancePoint(){
		int arr[] = {1,2,3};
		for(int i:arr){
			i = 10;	
		}
		System.out.println(arr[0]);
		System.out.println(arr[1]);
		System.out.println(arr[2]);
		
		
		List list = new ArrayList();
		list.add("1");
		for(Object obj:list){
			obj = "10";
		}
		System.out.println("--------------------");
		System.out.println(list.get(0));
	}
}

增强for循环学习笔记

标签：增强for循环   for   java   

原文地址：http://blog.csdn.net/xlgen157387/article/details/39272551