增强for循环学习笔记

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));
}
}