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MapTest.java
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110 lines (98 loc) · 3.01 KB
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import org.junit.Test;
import java.util.*;
/**
* @ Description:Map接口常用方法（以HashMap为例）
* 常用方法（HashMap为例）
* <p>
* 增：`put(Object key,Object value)`
* <p>
* 删：`remove(Object key)`
* <p>
* 改;`put(Object key,Object value)`
* <p>
* 查:`get(Object key)`
* <p>
* 长度:`size()`
* <p>
* 遍历:`keySet(), values(), entrySet()`
* @ Author: Jay
* @ Date: Create in 11:05 2021/4/15
* @ Version:
*/
public class MapTest {
@Test
public void MapTest1() {
Map map = new HashMap();//没要求泛型时，不要求key类型相同
//put()
map.put("AA", 1);
map.put("BB", 2);
map.put("CC", 1);
map.put("ab", 21);
map.put("AA", 110);//如果key存在，则修改
System.out.println(map);
Map map1 = new HashMap();
map1.put("DD", 45);
map1.put("EE", 43);
//putAll(map)
map1.putAll(map);
System.out.println(map1);
//remove(key),返回删除元素的value
Object value = map1.remove("DD");
System.out.println(value);
//clear()
map.clear();//map = null,但还在
System.out.println(map.size());//0
System.out.println(map);//{}
//isEmpty()
System.out.println(map.isEmpty());
//查询
//get(key)
System.out.println(map1.get("AA"));
System.out.println(map1.get("MM"));//不存在返回：null
//containsKey(key)
System.out.println(map1.containsKey("AA"));
//containsValue(value)
System.out.println(map1.containsValue(1));
//size()
System.out.println("size:" + map1.size());
//equals()
}
//遍历（掌握）
@Test
public void MapTest2() {
Map map = new HashMap();
map.put("AA", 1);
map.put("BB", 2);
map.put("CC", 3);
map.put("ab", 4);
//遍历所有key集合：keySet()
Set set = map.keySet();
Iterator iterator = set.iterator();
while (iterator.hasNext())
System.out.println(iterator.next());
//遍历所有的Values
Collection values = map.values();
for (Object obj : values) {
System.out.println(obj);
}
//遍历所有key-value
//方式一：entrySet()
Set entrySet = map.entrySet();
Iterator iterator1 = entrySet.iterator();
while (iterator1.hasNext()) {
//System.out.println(iterator1.next());//直接输出Node
Object obj = iterator1.next();
//entrySet集合长得元素都是entry
Map.Entry entry = (Map.Entry) obj;
System.out.println(entry.getKey() + "-->" + entry.getValue());
}
//方式二：分别取
Set keyset = map.keySet();
Iterator iterator2 = keyset.iterator();
while (iterator2.hasNext()) {
Object key = iterator2.next();
Object value = map.get(key);
System.out.println(key + "--->" + value);
}
}
}