使用泛型的数组列表实现，其中列表的最大大小是动态的

Question

I want to ask if someone knows how to fix this. I am getting this message:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
    at Main.add(Main.java:40)  // it is for: myList[actSize++] = object;
    at Main.main(Main.java:127) //it is for: ob.add(str+str1+str2); 

I want to ask if what i am doing is right. I would like to build a programm that uses generics with the following: methods add,remove,get,contains and size. But when I built the program I found out that the generics cannot create an array, so I used from another post in this site: [How to: generic array creation and used the weak typing (unchecked). So the main theme of this program is someone to type in console his first name last and his phone number and then to put it in array of generics so I could save it into an object and then into a specific position. After that the program dynamically increases the threshold in order for the user to have a lot of contacts. Then he wil be told if his contact has been duplicated and it will be removed immediatly. After he will be asked if he want to remove a contract and then the program stats all over, until the user finishes his job(adding contracts).

I would be glad to hear some opinions.

(I am sorry for my English if I am not understandable.)

import java.util.Arrays;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main < T >
{

    private Object[] myList;
    public static int actSize = 0;

    public Main(int s)
    {
        myList = new Object[s];
    }

    public T Array(int i)
    {
        @SuppressWarnings("unchecked")
        final T t = (T) myList[i];
        return t;
    }

    public void add(T object) //end
    {
        if (myList.length - actSize <= 5)
        {
            myList = Arrays.copyOf(myList, myList.length * 2);
            System.out.println("\nNew length: " + myList.length);
        }

        myList[actSize++] = object;
    }

    public void add(T object, int position) //end
    {
        myList[position++] = object;
    }

    public boolean remove(T object) //end
    {
        if (myList[actSize].equals(object))
        {
            myList[actSize] = myList[actSize - 1];
            return true;
        }
        else
            return false;
    }

    public void remove(int position) //end
    {
        myList[position] = myList[position - 1];
    }

    @SuppressWarnings("unchecked")
    public T get(int index) //end
    {
        if (index < actSize)
        {
            return (T) myList[index];
        }
        else
        {
            throw new ArrayIndexOutOfBoundsException();
        }
    }

    public boolean contains(T object) //end
    {
        if (myList[actSize].equals(object))
        {
            return false;
        }
        else
            myList[actSize] = myList[actSize - 1];

        return true;
    }

    public int size() //end
    {
        return actSize;

    }

    @SuppressWarnings("unchecked")
    public static void main(String[] args)
    {
        @SuppressWarnings("rawtypes")
        Main ob = new Main(actSize);
        String str, str1, str2;

        try
        {
            BufferedReader br = new BufferedReader(new InputStreamReader(System. in ));

            while (true)
            {
                System.out.print("Do you want to add a contact? press any key to continue or n to exit :");
                String str5 = br.readLine();

                if ("n".equalsIgnoreCase(str5))
                {
                    System.exit(1);
                }

                System.out.print("Enter your First Name :");
                str = br.readLine();

                System.out.print("Enter your Last Name :");
                str1 = br.readLine();

                System.out.print("Enter your Phone Number :");
                str2 = br.readLine();

                ob.add(str + str1 + str2);
                ob.add(str + str1 + str2, actSize);

                if (ob.contains(str + str1 + str2) == true)
                {
                    System.out.println("The contact you entered is duplicated");
                    ob.remove(ob.contains(str + str1 + str2));
                    System.out.println("The contact has been removed");
                }

                System.out.print("Do you want to add contracts? press y to continue :");
                String str3 = br.readLine();
                System.out.println("You just entered:" + str3);

                if ("y".equalsIgnoreCase(str3))
                {
                    System.out.print("Which contract do you wish to be removed?");
                    String str4 = br.readLine();

                    if (str4.equals(actSize))
                    {
                        ob.remove(actSize);
                        System.out.println("The contact has been deleted.");
                    }
                }
            }
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
    }

}

Answer 1

Why not using List<YourGenericType> list = new ArrayList<YourGenericType>(); now you can call list.size(); list.add(); list.set(); list.get();... list.size(); list.add(); list.set(); list.get();... list.size(); list.add(); list.set(); list.get();... . Also ArrayList have a dynamic size.

I suggest something like this: delete your Main and change your main method to something like this:

import java.util.*;
import java.io.*;

public class Test {

    public static void main(String[] args) {

        List<String> list = new ArrayList<String>();
        String str, str1, str2;
        try {
            BufferedReader br = new BufferedReader(new InputStreamReader(
                    System.in));
            while (true) {

                System.out
                        .print("Do you want to add a contact? press any key to continue or n to exit :");
                String str5 = br.readLine();

                if ("n".equalsIgnoreCase(str5)) {
                    System.exit(1);
                }

                System.out.print("Enter your First Name :");
                str = br.readLine();

                System.out.print("Enter your Last Name :");
                str1 = br.readLine();

                System.out.print("Enter your Phone Number :");
                str2 = br.readLine();

                StringBuilder sb = new StringBuilder();
                sb.append(str + str1 + str2);

                for (int i = 0; i < list.size(); i++) {
                    String s = list.get(i);
                    if (s.equals(sb.toString())) {
                        System.out.println("Duplicate");
                        list.remove(i);
                    }
                }
                list.add(sb.toString());

                System.out
                        .print("Do you want to add contracts? press y to continue :");
                String str3 = br.readLine();
                System.out.println("You just entered:" + str3);

                if ("y".equalsIgnoreCase(str3)) {
                    System.out
                            .print("Which contract do you wish to be removed?");
                    String str4 = br.readLine();

                    int index = Integer.parseInt(str4);
                    if (index < list.size() && index > 0) {
                        list.remove(index);
                    }

                }

            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

Answer 2

First, you can use List to store unknown amount of data.

For your code:

myList[actSize++] = object;

throws exception because myList is initialized with 0 length. So you cannot put anything in index 0.