- 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 :
- Declare the array private Student studentList[]; this declares studentList
- Create the array studentList = new Student[10]; this sets up 10 spaces in memory that can hold references to Student objects
- 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); } }