java 遍历List 和 Map的几种方法

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java遍历List

1、（性能最差）

1. for(String tmp:list)
2. {
3. //System.out.println(tmp);
4. }

2、（性能最好）

1. for(int i = 0; i < list.size(); i++)
2. {
3. list.get(i);
4. //System.out.println(list.get(i));
5. }

3、

1. Iterator<String> iter = list.iterator();
2. t1=System.currentTimeMillis();
3. while(iter.hasNext())
4. {
5. iter.next();
6. //System.out.println(iter.next());
7. }

java中遍历Map

第一种用for循环 
Java代码 

for(Map.Entry<String, String> entry:map.entrySet()){    
     System.out.println(entry.getKey()+"--->"+entry.getValue());    
}   
for(Map.Entry<String, String> entry:map.entrySet()){ 
          System.out.println(entry.getKey()+"--->"+entry.getValue()); 
} 

第二种用迭代 
Java代码 

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());    
}   
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 

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);    
}   
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 

Iterator it=map.entrySet().iterator();           
System.out.println( map.entrySet().size());    
String key;           
String value;    
while(it.hasNext()){    
        Map.Entry entry = (Map.Entry)it.next();           
        key=entry.getKey().toString();           
        value=entry.getValue().toString();           
        System.out.println(key+"===="+value);                     
}