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/**
 * Collection
 */
public interface Collection {

    public void add(Object element);
    public void remove(Object element);
    public boolean isEmpty();
    public boolean contains(Object element);
    public int size();
    public void removeAll(Object e);
    public int frequency(Object e);
    public String toString();
}

import java.util.Arrays;

/**
 * ArrayCollection
 */
public class ArrayCollection implements Collection{

    private Object[] elementData;
    private int size;
    public ArrayCollection(int c){
        elementData = new Object[c];
        size=0;
    }
    public ArrayCollection(){
        elementData = new Object[0];
        size=0;
    }
    public void add(Object e) {
        if(e == null) throw new IllegalArgumentException();
        ensureCapacity(size+1);
        elementData[size++] = e;
    }
    public int size(){
        return size;
    }
    public boolean isEmpty() {
        return size == 0;
    }
    public boolean contains(Object e) {
        return indexOf(e) != -1;
    }
    public void remove(Object e) {
        int i = indexOf(e);
        if (i != -1) {
            elementData[i] = elementData[--size];
            elementData[size] = null;
        }
    }
    private int indexOf(Object e) {
        for (int i=0; i<size; i++){
            if(elementData[i].equals(e)) return i;
            }
            return -1;
    }
    private void ensureCapacity(int capacity) {
        if (capacity > elementData.length) {
            int s = Math.max(capacity, 2*elementData.length);
            Object[] arr = new Object[s];
            for(int i = 0; i < size; i++)
                arr[i] = elementData[i];
            elementData = arr;
        }
    }
    public void removeAll(Object e) {
        for (int i = 0; i < size; i++) {
            if(elementData[i].equals(e)) remove(elementData[i]);
        }
    }
    public int frequency(Object e) {
        int counter=0;
        for (int i = 0; i < size; i++) {
            if(elementData[i].equals(e)) counter++;
        }
        return counter;
    }
    public String toString() {
        String result = "[";
        for (int i = 0; i < size; i++) {
            result+=elementData[i];
            if(i!=size-1){
                result+=",";
            }
        }
        result+="]";
        return result;
    }
}

/**
 * main
 */
public class main {

    public static void main(String[] args) {
        Collection name = new ArrayCollection();
        name.add("AJ");
        name.add("CK");
        name.add("TJ");
        name.add("CK");
        name.add("MP");
        name.add("GG");
        name.add("AJ");
        name.add("SB");
        name.add("AJ");
        System.out.println(name.toString());
        System.out.println("num AJ: "+name.frequency("AJ"));
        name.removeAll("AJ");
        System.out.println(name.toString());
    }
}