Java Treemap和ArrayList传输项

Question

I have the following code, a Treemap with a arraylist of fruits. In the removeAndAdd function, I would like to remove [apple,orange] and add it into bList of the container 2. but the display came out with additional bracket []. Is my method correct?

public class TreeMapEx {

  private TreeMap<Integer, List<String>> tMap = new TreeMap<Integer, List<String>>();
  private List<String> aList = new ArrayList<String>();
  private List<String> bList = new ArrayList<String>();
    public static void main(String[] args) {
       TreeMapEx tm = new TreeMapEx();
        tm.addToTree();
        tm.addToList(1);
        tm.showItem(1);       
        tm.showItem(2);
        tm.removeAndAdd(1);
        tm.showItem(2);

    }

    private void addToTree() {
        tMap.put(1, aList);        
        bList.add("dragonfruit");
        tMap.put(2, bList);

    }

    private void addToList(int item) {
        if (tMap.containsKey(item)) {
            aList = new ArrayList<String>();
            aList.add("apple");
            aList.add("orange");
            tMap.put(item, aList);
            System.out.println(item + " added");
        } else {
            System.out.println(item + " not found");
        }
    }

    private void showItem(int item){

        System.out.println(item+" contain " + tMap.get(item));
    }

      private void removeAndAdd(int item){
          if (tMap.containsKey(item) && tMap.containsValue(aList)) {
          //remove everything from 1 and add to 2
           aList = new ArrayList<String>();
             List<String> temp;
             temp = tMap.get(item);

             bList.add(temp.toString());
          }         
    }

}

Output:
1 added
1 contain [apple, orange]
2 contain [dragonfruit]
2 contain [dragonfruit, [apple, orange]]

How to remove the additional bracket of [apple, orange] in container 2.

To something like this

1 added
1 contain [apple, orange]
2 contain [dragonfruit]
2 contain [dragonfruit,apple, orange]

Answer 1

Additional bracket of [apple, orange] is printing becaus the following code is used in method showItem .

System.out.println(item+" contain " + tMap.get(item));

It is equal to print the elements of List using the following code.

System.out.println(item+" contain " + tMap.get(item).toString() );

Note: tMap.get(item) is a List type (List)

If you want to display the elements without additional bracket. You can use the following code:

    private void showItem(int item){
        System.out.println(item+" contain ");
        for(String str:tMap.get(item) )
        {
            System.out.println( str);
        }
    } 

In addition, one more thing is not using correctly. Please refer to method removeAndAdd .

Change bList.add(temp.toString()) ; to bList.addAll(temp) ;

If you use bList.add(temp.toString()), List elements with [apple, orange] will be added to bList as a string. Actually, you would like to add it with apple and orange seperately. Use bList.addAll(temp) ;

To see why Collection, such as List print additional bracket is added . Please refer to the source code of java.util.AbstractCollection , which overrides toString method. Code is as follows:

public String toString() {
    Iterator<E> it = iterator();
    if (! it.hasNext())
        return "[]";

    StringBuilder sb = new StringBuilder();
    sb.append('[');
    for (;;) {
        E e = it.next();
        sb.append(e == this ? "(this Collection)" : e);
        if (! it.hasNext())
            return sb.append(']').toString();
        sb.append(',').append(' ');
    }
}