HashMap簡單說明:
1>key是用Set來存放的,不可重複。value是用Collection來存放的,可重複。一個key-value對,是一個Entry。所有的Entry是用Set存放的,也是不可重複的。
2>向HashMap中添加元素時,會調用key所在類的equals()方法,判斷兩個key是否相同。若相同則只能添加進後添加的那個元素。
HashMap插入、遍歷 實例:
package com.lin.map;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
public class Test_HashMap {
public static void main(String[] args) {
Map<String,String> hashMap = new HashMap<String,String>();
hashMap.put("AA", "AA_Value");
hashMap.put("BB", "BB_Value");
hashMap.put("CC", "CC_Value");
//遍歷鍵
Set<String> keySet = hashMap.keySet();
Iterator<String> iterator = keySet.iterator();
while(iterator.hasNext()){
System.out.println(iterator.next());
}
System.out.println("============================");
//遍歷值
Collection<String> valueColl = hashMap.values();
Iterator<String> iterator1 = valueColl.iterator();
while(iterator1.hasNext()){
System.out.println(iterator1.next());
}
System.out.println("============================");
//遍歷鍵值對
Set< Entry<String,String> > entry = hashMap.entrySet();
//方式一:
Iterator< Entry<String,String> > iterator3 = entry.iterator();
while(iterator3.hasNext()){
Entry<String,String> key_value = iterator3.next();
System.out.println(key_value.getKey()+"------------->" + key_value.getValue());
}
System.out.println();
//方式二:
for(Entry<String,String> e : entry){
System.out.println(e.getKey()+"----->"+e.getValue());
}
}
}