Példák az ArrayList és a generics használatára

"Mit szólnál, ha azzal kezdeném, ami valójában hasznos? Most látni fogsz néhány módszert, amellyel az ArrayList és a generikusok használhatók:

"1. példa:"

public static void main(String[] args) throws IOException
{
    BufferedReader reader = new BufferedReader(new InputStreamReader(System.in) );
    ArrayList<Integer> list = new ArrayList<Integer>() ;

    while (true)
    {
        String s = reader.readLine();
        if (s.isEmpty()) break;
        list.add(Integer.parseInt(s));
    }
}

"2. példa:"

public static void main(String[] args) throws IOException
{
    BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    ArrayList<Integer> list = new ArrayList<Integer>();

    while (true)
    {
        String s = reader.readLine();
        if (s.isEmpty()) break;

        int x = Integer.parseInt(s);
        if (x % 2 == 0)  // Check that the remainder is zero when we divide by two
            list.add(x);         // Add to the end
        else
            list.add(0, x);      // Add to the beginning
    }
}

"3. példa:"

public static void main(String[] args) throws IOException
{
    BufferedReader reader = new BufferedReader(new InputStreamReader(System.in) );
    ArrayList<Integer> list = new ArrayList<Integer>();

    list.add(1);
    list.add(7);
    list.add(11);
    list.add(3);
    list.add(15);

    for (int i = 0; i < list.size(); ) // We moved the statement that increases i to inside the loop
    {
        if (list.get(i) > 5)
            list.remove(i);  // Don’t increase i if we deleted the current element
        else
            i++;
    }
}

"4. példa:"

public static void main(String[] args) throws IOException
{
    // Static initialization of the array
    int[] data = {1, 5, 6, 11, 3, 15, 7, 8};

    // Create a list where all elements are Integers
    ArrayList&ltInteger> list = new ArrayList&ltInteger> ();

    // Use the array to fill the list
    for (int i = 0; i < data.length; i++) list.add(data[i]);

    ArrayList&ltInteger> even = new ArrayList&ltInteger>();  // Even numbers
    ArrayList&ltInteger> odd = new ArrayList&ltInteger>();    // Odd numbers

    for (int i = 0; i < list.size(); i++)
    {
        Integer x = list.get(i);
        if (x % 2 == 0)    // If x is even
            even.add(x);   // Add x to the collection of even numbers
        else
            odd.add(x);    // Add x to the collection of odd numbers
    }
}

"5. példa:"

public static void main(String[] args) throws IOException
{
    ArrayList<Integer> list1 = new ArrayList<Integer>();   // Create a list
    Collections.addAll(list1, 1, 5, 6, 11, 3, 15, 7, 8);   // Fill the list

    ArrayList<Integer> list2 = new ArrayList<Integer>();
    Collections.addAll(list2, 1, 8, 6, 21, 53, 5, 67, 18);

    ArrayList<Integer> result = new ArrayList<Integer>();

    result.addAll(list1);   // Add all values from each list to the new list
    result.addAll(list2);

    for (Integer x : result)   // A fast way to loop over all elements, only for collections
    {
        System.out.println(x);
    }
}

"Jó! Diego most ad nekem egy teherautónyi hasonló gyakorlatot?"

"Igen, ő fog."