在Java中将Map键值从一个类复制到另一个类

Question

请有人帮我在 Java 中将 Map 键值从一个类复制到另一个类。

例子：

            public class FirstClass
            {   
               public static Map<String, Integer> firstMethod()
               {
                  Map<String, Integer> firstMap = new HashMap <String, Integer>();
                  firstMap.put("1234", 1000000);
                  firstMap.put("2345", 2000000);
                  firstMap.put("3456", 3000000);
                  firstMap.put("4567", 4000000);
                  return firstMap;
               }   
            }

   public class SecondClass

           public SecondClass()
           {
             instanceSet = new HashSet<ThirdClass>();
           }

      public void addInstance(String string)
       {
         ThirdClass integer = new ThirdClass(string);
         instanceSet.add(integer);     
       }   

       public void someMethod(Map<String, Integer> secondMap)
               {
                  for (ThirdClass instance : instanceSet)
                  {
                     if(secondMap.containsKey(instance.getinstanceNumber()))
                     {
                       //what should go in here??
                     }  
                  }   
               }  

本质上，如果 instanceSet 包含在 firstMap 中找到的键，那么如何提取该键的 Integer 值并将其复制到 secondMap 中相同键的 Integer 值？

我在网上环顾四周，但我发现的所有代码示例似乎都不起作用，因为地图存储在单独的类中。

Answer 1

像这样的代码。 您需要在someMethod引用firstMap ，反之亦然，具体取决于您要从哪里复制到哪里。

if(secondMap.containsKey(instance.getinstanceNumber())) {
       firstMap.put(instance.getinstanceNumber(), secondMap.get(instance.getinstanceNumber()));
} 

---

像这样的东西——

public class FirstClass {
    public Map<String, Integer> firstMap;

    public FirstClass() {
        firstMap = new HashMap <String, Integer>();
        firstMap.put("1234", 1000000);
        firstMap.put("2345", 2000000);
        firstMap.put("3456", 3000000);
        firstMap.put("4567", 4000000);
    }

    public void updateMap(String key, Integer value) {
        firstMap.put(key, value);
    }
}

public class SecondClass {

    private Set<ThirdClass> instanceSet;
    private FirstClass firstClass;

    public SecondClass() {
        instanceSet = new HashSet<ThirdClass>();
        firstClass = new FirstClass();
    }

    public void addInstance(String string) {
        ThirdClass integer = new ThirdClass(string);
        instanceSet.add(integer);
    }

    public void someMethod(Map<String, Integer> secondMap) {
        for (ThirdClass instance : instanceSet) {
            if (secondMap.containsKey(instance.getinstanceNumber())) {
                firstClass.updateMap(instance.getinstanceNumber(), secondMap.get(instance.getinstanceNumber()));
            }
        }
    }
}