Arrays In Java

Posted in: ArrayList with Examples,Core Java,Core Java Test 1,JAVA/J2EE,Using Array in JSP

• An array is a list of similar things
• An array has a fixed: name , type and length
• These must be declared when the array is created.
• Arrays sizes cannot be changed during the execution of the code

myArray has room for 8 elements.The elements are accessed by their index

in Java, array indices start at 0

Declaring Arrays :

int myArray[]:

declares myArray to be an array of integers

myArray = new int[8]:

sets up 8 integer-sized spaces in memory, labelled myArray[0] to myArray[7]

int myArray[] = new int[8]:

combines the two statements in one line.

Assigning Values:

refer to the array elements by index to store values in them.

myArray[0] = 3;

myArray[1] = 6;

myArray[2] = 3;   ...

can create and initialise in one step:

int myArray[] = {3, 6, 3, 1, 6, 3, 4, 1};

Iterating Through Arrays

for loops are useful when dealing with arrays:

for (int i = 0; i < myArray.length; i++) {

  myArray[i] = getsomevalue();

}

Arrays of Objects:

• So far we have looked at an array of primitive types.

           -> integers

           -> could also use doubles, floats, characters…

• Often want to have an array of objects

         Ex: Students, Books, Loans 

• Need to follow 3 steps

Declaring the Array :

1. Declare the array                                                                    private Student studentList[]; this declares studentList 
2. Create the array                                                                              studentList = new Student[10];                                                        this sets up 10 spaces in memory that can hold references to Student objects
3. Create Student objects and add them to the array:                          studentList[0] = new Student("Cathy", "Computing");

Sample Example:

class ArraysExample{
 public static void main(String[] args) {
  int[] ia = new int[101];
  for (int i = 0; i < ia.length; i++)
   ia[i] = i;
  int sum = 0;
  for (int i = 0; i < ia.length; i++)
   sum += ia[i];
  System.out.println(sum);
 }
}