import java.util.HashMap;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;
public class MapOperate{
Map<String, String> map = new HashMap<String, String>();//定義一個key和value都爲String類型的HashMap
Hashtable<String, String> table = new Hashtable<String, String>();//定義一個key和value都爲String類型的Hashtable
map.put("1", "value1");
map.put("2", "value2");
map.put("3", "value3");
//第一種:普遍使用,二次取值
System.out.println("通過Map.keySet遍歷key和value:");
for (String key : map.keySet()) {
System.out.println("key= "+ key + " and value= " + map.get(key));
}
//第二種
System.out.println("通過Map.entrySet使用iterator遍歷key和value:");
Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<String, String> entry = it.next();
System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
}
//第三種:推薦,尤其是容量大時
System.out.println("通過Map.entrySet遍歷key和value");
for (Map.Entry<String, String> entry : map.entrySet()) {
System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
}
//第四種
System.out.println("通過Map.values()遍歷所有的value,但不能遍歷key");
for (String v : map.values()) {
System.out.println("value= " + v);
}
}
HashMap是線程不安全的,key和value允許爲null
public V get(Object key){
…
}
public V put(K key, V value){
…
}
HashTable是線程安全的(synchronized),key和value不能爲null,方法是同步鎖的
public synchronized V get(Object key){
…
}
public synchronized V put(K key, V value){
…
}
public synchronized V remove(Object key){
…
}