java map中相同的key保存多个value值方式

package test; 
import org.junit.Test; 
import java.util.HashMap;
import java.util.IdentityHashMap;
import java.util.Map; 
import static java.util.Objects.hash; 
public class HashMapTest {
 
    @Test
    public void test0() {
        String str1 = new String("key");
        String str2 = new String("key");
        System.out.println(str1 == str2);
 
        Map<String,String> map = new HashMap<String,String>();
        map.put(str1,"value1");
        map.put(str2,"value2");//会覆盖之前的值，map长度为1
        
 
        for(Map.Entry<String,String> entry:map.entrySet()){
            System.out.println(entry.geTKEy()+"  "+entry.getValue());
        }
        System.out.println("------->"+map.get("key"));
    }
控制台输出如下： 
 
    
    @Test
    public void test1(){
        String str1 = "key";
        String str2 = "key";
        System.out.println(str1 == str2);
        Map<String,String> map = new IdentityHashMap<>();
        map.put(str1,"value1");
        map.put(str2,"value2");
        for(Map.Entry<String,String> entry:map.entrySet()){
            System.out.println(entry.getKey()+"  "+entry.getValue());
        }
        System.out.println("containsKey---->"+map.get("key"));
        System.out.println("value---->"+map.get("key"));
    }
 控制台输出如下 
 
 
 
    @Test
    public void test2(){
        String str1 = new String("key");
        String str2 = new String("key");
        System.out.println(str1 == str2);
        Map<String, String> map = new IdentityHashMap<>();
        map.put(str1,"value1");
        map.put(str2,"value2");
        for(Map.Entry<String,String> entry:map.entrySet()){
            System.out.println(entry.getKey()+"  "+entry.getValue());
        }
        System.out.println("\"key\" containKey--->"+map.containsKey("key"));
        System.out.println("str1 containKey--->"+map.containsKey(str1));
        System.out.println("str2 containKey--->"+map.containsKey(str2));
        System.out.println("value--->"+map.get("key"));
        System.out.println("value--->"+map.get(str1));
        System.out.println("value--->"+map.get(str2));
    }
 控制台输出如下：
 
  
 
    
    private class CustomObject{
        private String value; 
        public CustomObject(String value){
            this.value = value;
        }
 
        public String getValue() {
            return value;
        }
 
        public void setValue(String value) {
            this.value = value;
        }
 
         
 
        @Override
        public int hashCode() {
            if(value !=null){
                return super.hashCode()+hash(value);
            }else{
                return super.hashCode();
            }
        }
 
        @Override
        public boolean equals(Object obj) {
            if(this == obj){
                return true;
            }
            if(obj == null || getClass() != obj.getClass()){
                return false;
            }
            CustomObject object = (CustomObject) obj;
            if(this.value != null && this.value.equals(object.getValue())){
                return true;
            }
            if(this.value == null && object.value == null){
                return true;
            }
            return false;
        }
    } 
}

public static void main(String[] args) {
	Map<String, Object> identity = new IdentityHashMap<>();
	identity.put("A", "A");
	identity.put("A", "B");
	identity.put("A", "C");
	Map<String, Object> identityString = new IdentityHashMap<>();
	identityString.put(String.join("A", ""), "B");
	identityString.put("A", "A");
	identityString.put(new String("A"), "C");
	MultiValueMap<String, Object> linked = new LinkedMultiValueMap<>();
	linked.add("A", "A");
	linked.add("A", "B");
	linked.add("A", "C");
	for (String key : identity.keySet()) {
		System.out.println("identity:" + identity.get(key));
	}
	for (String key : identityString.keySet()) {
		System.out.println("identity string:" + identityString.get(key));
	}
	for (String key : linked.keySet()) {
		System.out.println("linked:" + linked.get(key));
	}
}

static class Entry<K, V> extends HashMap.node<K, V> { Entry<K, V> before; Entry<K, V> after; }