Arrays in java

Array:

• Array is referenced data type used to store multiple values.
• we can not change size of array at runtime.
• memory can not be altered Once the memory has been allocated for an array at the run time.
• Arrays are objects

Need of array:

• In  real time projects array is used to collect same type of objects to send all values with single method call.

Problem of primitive data types:

• We can not store values in continuous memory locations using primitive data types .
• We have two problems due to this limitation

1.we cant store multiple values:

• If we want to store multiple values , say 1 to 10 , we must create 10 variables .
• All those 10 variables are created at different locations.

2.In single method call we can not pass multiple values :

• we can not pass all values to the remote computer with single network call or method call.Using primitive variables  , which increases burden on network and also increase number of lines of code in program.

Solution:

• Values must be stored in continuous memory locations with single variable name. To solve above two problems ,
• This can be possible using array.
• In java array is reference data type . it is used to store fixed number of multiple values of same type in continuous memory locations.
• Like other data types array is not a keyword it is a concept. it creates continuous memory locations using other primitive or reference types.

 Array Limitation: 

•  Array size is fixed , means we can not increase or decrease its size after its creation.

Array Declaration:

• <Accessibility modifier><Modifier><datatype>[] <array variable name>;

For example:

• public static int[] i;
• public static Example[] e;
• Like in C or C++ , in java we can not mention array size in declaration part. It leads Compile time error.
• int[5] i; Compile time Error: illegal start of expression
• int [] i;

Possible declaration:

1. After data type : int[] i;
2. Before variable name : int []i;
3. After variable name : int i[];

Type of arrays:

1.  Single dimensional : int [] i;
2. Two dimensional : int[][] i;
3. Three dimensional : int [][][] i;

Array object creation:

• <Accessibility Modifier><Modifier><data type>[]<array name>={<list of values with , separator>};
• int [] ia={10,20,30,40};