Arrays and Collection Framework

Arrays and Collection Framework

1. Arrays:

Declaration:

type arrName[];
OR
type[] arrName;

Instantiation:

arrName = new type[size];

Can be combined in one statement:

type[] myArray = new type[size];

If elements are already known, declaration/instantiation can be done in the following way:

int[] nums = {1, 2, 1, 1, 3};

Accessing and Editing Elements:

String[] cities = {"Eskisehir", "Istanbul", "Izmir"};
System.out.println(cities[0]);

cities[0] = "Ankara";

2. Multidimensional Arrays:

Declaration and Instantiation:

Similar to a 1D array but adding more dimensions:

Syntax:

data_type[1st dimension][2nd dimension][]..[Nth dimension] 
array_name = new data_type[size1][size2]….[sizeN];

As an example:

int[][] intArray = new int[10][20]; //a 2D array or matrix
int[][][] intArray = new int[10][20][10]; //a 3D array

Same as 1D arrays, if the elements are known declaration can be done in the following manner: (R1C1 corresponds to row 1 column 1)

data_type[][] arrName = {
                        {valueR1C1, valueR1C2, ....}, 
                        {valueR2C1, valueR2C2, ....}
                        };

We can use nested loops to add elements to a multi-dimensional array, as an example:

for (int i = 1; i <= 9; i++) {
       for (int j = 1; j <= 9; j++) {
            intArray[i][j] = i*j;
       }
}

3. ArrayList:

ArrayLists are dynamic, unlike arrays. This makes them easier to use when there will be lots of manipulations to the array (adding and deleting many elements)

ArrayList<Type> arrName = new ArrayList<Type>();

4. LinkedList:

LinkedList<Type> linkedListName = new LinkedList<Type>();

5. Stack and Queue:

6. Set (HashSet):

7. Map (HashMap):