List 遍历三种

List<String> list = new ArrayList<String>();
list.add("aaa");
list.add("bbb");
list.add("ccc");
方法一：
超级for循环遍历
for(String attribute : list) {
  System.out.println(attribute);
}
方法二：
对于ArrayList来说速度比较快, 用for循环, 以size为条件遍历:
for(int i = 0 ; i < list.size() ; i++) {
  system.out.println(list.get(i));
}
方法三：
集合类的通用遍历方式, 从很早的版本就有, 用迭代器迭代
Iterator it = list.iterator();
while(it.hasNext()) {
  System.ou.println(it.next);
}

publicstaticvoid main(String[] args) {

List l = new ArrayList();

l.add("世界你好！");

l.add("上海");

for (int i = 0; i < l.size(); i++) { // 普通的for循环取出集合中的元素

System.out.print(l.get(i));

 

}

System.out.println();

for (Object o : l) { // 增强for循环取出集合中的元素

System.out.print(o);

}

System.out.println();

for (Iterator it = l.iterator(); it.hasNext();) { // 利用迭代器取出集合中的元素

 

System.out.print(it.next());

 

}

 

System.out.println();

Iterator it = l.iterator(); //利用迭代器取出集合中的元素

while (it.hasNext()) {

System.out.print(it.next());

 

}

 

}

 

}

 

java中遍历MAP的几种方法

 

1. Map<String,String> map=new HashMap<String,String>();

2. map.put("username", "qq");

3. map.put("passWord", "123");

4. map.put("userID", "1");

5. map.put("email", "qq@qq.com");

 

Map<String,String> map=new HashMap<String,String>();

map.put("username", "qq");

map.put("passWord", "123");

map.put("userID", "1");

map.put("email", "qq@qq.com");

 

 

第一种用for循环

Java代码

 

1. for(Map.Entry<String, String> entry:map.entrySet()){

2. System.out.println(entry.getKey()+"--->"+entry.getValue());

3. }

 

for(Map.Entry<String, String> entry:map.entrySet()){

System.out.println(entry.getKey()+"--->"+entry.getValue());

}

 

 

 

第二种用迭代

Java代码

 

1. Set set = map.entrySet();

2. Iterator i = set.iterator();

3. while(i.hasNext()){

4. Map.Entry<String, String> entry1=(Map.Entry<String, String>)i.next();

5. System.out.println(entry1.getKey()+"=="+entry1.getValue());

6. }

 

Set set = map.entrySet();

Iterator i = set.iterator();

while(i.hasNext()){

Map.Entry<String, String> entry1=(Map.Entry<String, String>)i.next();

System.out.println(entry1.getKey()+"=="+entry1.getValue());

}

 

 

用keySet()迭代

Java代码

 

1. Iterator it=map.keySet().iterator();

2. while(it.hasNext()){

3. String key;

4. String value;

5. key=it.next().toString();

6. value=map.get(key);

7. System.out.println(key+"--"+value);

8. }

 

Iterator it=map.keySet().iterator();

while(it.hasNext()){

String key;

String value;

key=it.next().toString();

value=map.get(key);

System.out.println(key+"--"+value);

}

 

 

 

用entrySet()迭代

Java代码

 

1. Iterator it=map.entrySet().iterator();

2. System.out.println( map.entrySet().size());

3. String key;

4. String value;

5. while(it.hasNext()){

6. Map.Entry entry = (Map.Ent

 

ry)it.next();

7. key=entry.getKey().toString();

8. value=entry.getValue().toString();

9. System.out.println(key+"===="+value);

10. }

 

package com.sina.www;

import java.util.HashMap;

import java.util.Iterator;

import java.util.Map;

import java.util.Set;

public class MapTest2 {

public static void main(String[] args) {

Map<String, String> m = new HashMap<String, String>();

// m.put(001, new Person("关羽", 23));

// m.put(002, new Person("刘备", 24));

// m.put(003, new Person("百度", 22));

//

m.put("sa", "123");

m.put("sb", "143");

m.put("sc", "153");

m.put("sd", "184");

Set keyset = m.keySet(); // 对Map集合的迭代方法一keyset 迭代

Iterator it = keyset.iterator();

while (it.hasNext()) {

String p = (String) it.next();

System.out.print("value=" + m.get(p) + " ");

}

// System.out.println(m.get("sa"));

Iterator it2 = m.entrySet().iterator(); // Map集合的迭代方法二entrySet迭代

System.out.println();

System.out.println("长度为" + m.entrySet().size());

String key;

String value;

while (it2.hasNext()) {

Map.Entry entry = (Map.Entry) it2.next();

key = entry.getKey().toString();

value = entry.getValue().toString();

System.out.print(key + "=" + value + " ");

}

System.out.println();

System.out.println("------------------");

for (Map.Entry entry : m.entrySet()) { // // Map集合的迭代方法三for循环迭代

System.out.print(entry.getKey() + "=" + entry.getValue() + " ");

}

}