Java：从集合中删除元素

Question

I have a collection, and I want to implement the add() method, such that only positive integers can be added to the collection. The collection can hold 4 values, and I have used the code below to initialize every value as "-1".

  public class Bag implements Collection {


private int[] elements;

public Bag() {
    elements = new int[Runner.SIZE_OF_COLLECTION];
    for (int i = 0; i < Runner.SIZE_OF_COLLECTION; i++) {
        elements[i] = -1;
    }
}

So far in the method add() below, I have this loop iterating through each element in the collection, and replacing each element that's less than 0 with the positive integer that I want to add ("toAdd").

The problem is, I only want to add the positive integer "toAdd" once, and without a break in the loop, the method replaces EVERY element "-1" in the collection with the positive integer. With the break in the loop, the method fails to add the positive integer at all. Any ideas on how I can get the method to add the positive integer to the collection only once?

public void add(int toAdd) {
    for (int i = 0; i < Runner.SIZE_OF_COLLECTION; i++) {
        if (elements[i] <= 0 && toAdd>0) {
            elements[i] = toAdd;
            }
                        break;
    }
}

Thanks in advance!

Answer 1

将中断移动到if语句中。

Answer 2

You could use an ArrayList instead of an int array. With an ArrayList, you could get the index of the first occurence of -1 and use the set method to add your new value at that index.

Answer 3

This replaces the first value from elements , which is equal or less than 0, with value from toAdd argument.

public void add(int toAdd) {
    for (int i = 0; i < Runner.SIZE_OF_COLLECTION; i++) {
        if (elements[i] <= 0 && toAdd>0) {
            elements[i] = toAdd;
            break;
        }             
    }
}

Answer 4

The add method for the interface Collection takes an Object (or a generic type, which you have not specified). If you are trying to override / implement the collection interface method with your add method, then the method signature is incorrect, and it will never be called.

Your class needs to look like:

public class Bag implement Collection<Integer>
{
  // ... other necessary methods

  public boolean add(Integer i)
  {
    // your method...
  } 
}

And probably easier than your implementation would be to do:

public class Bag extends java.util.ArrayList<Integer>
{
  @Override
  public boolean add(Integer i)
  {
    if ((i != null) && (i > 0)) super.add(e);
  }
}

You probably need to override the other add methods as well, although truthfully, it would be better to encapsulate the ArrayList instead of extending it.