在Java中将Map键值从一个类复制到另一个类

Question

Please could anybody help me with copying a Map key value from one class to another in Java.

Example:

            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??
                     }  
                  }   
               }  

Essentially, if the instanceSet contains a key that is found in firstMap then how can the Integer value of that key be extracted and copied to the Integer value of the same key in secondMap?

I have looked around online but all of the code examples that I have found don't seem to work presumably because the maps are stored in separate classes.

Answer 1

Something like this code. You need the reference of firstMap in your someMethod or vice versa depending upon from where you want to copy to where.

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

---

Something like this -

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()));
            }
        }
    }
}