遍历Map的四种方法
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2024-02-17 14:59:52
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package com.bijian.study;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
public class HashMapTest {
public static void main(String[] args) {
Map<String, String> map = new HashMap<String, String>();
map.put("1", "value1");
map.put("2", "value2");
map.put("3", "value3");
//第一种:普遍使用,二次取值
System.out.println("通过Map.keySet遍历key和value:");
for (String key : map.keySet()) {
System.out.println("key= " + key + " and value= " + map.get(key));
}
//第二种
System.out.println("通过Map.entrySet使用iterator遍历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());
}
//第三种:推荐,尤其是容量大时
System.out.println("通过Map.entrySet遍历key和value");
for (Map.Entry<String, String> entry : map.entrySet()) {
System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
}
//第四种
System.out.println("通过Map.values()遍历所有的value,但不能遍历key");
for (String v : map.values()) {
System.out.println("value= " + v);
}
}
}
运行结果:
通过Map.keySet遍历key和value: key= 3 and value= value3 key= 2 and value= value2 key= 1 and value= value1 通过Map.entrySet使用iterator遍历key和value: key= 3 and value= value3 key= 2 and value= value2 key= 1 and value= value1 通过Map.entrySet遍历key和value key= 3 and value= value3 key= 2 and value= value2 key= 1 and value= value1 通过Map.values()遍历所有的value,但不能遍历key value= value3 value= value2 value= value1
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