Abstract data types in java.

Java abstract data type(ADT) in a data structure is a type of data type whose behaviour is defined by a set of operations and values.

In Java abstract data type, we can only know what operations are to be performed and not how to perform them i.e. it does not tell how algorithms are to be implemented or how the data will be organized in the memory. This type is thus called abstract as it does not give the view of implementation.

The user of data type does not need to know how that data type is implemented, for example, we have been using Primitive values like int, float, char data types only with the knowledge that these data type can operate and be performed on without any idea of how they are implemented

Types of Abstract Datatypes.

List ADT

• The data is generally stored in key sequence in a list which has a head structure consisting of count, pointers and address of compare function needed to compare the data in the list.

• The data node contains the pointer to a data structure and a self-referential pointer which points to the next node in the list.

The List ADT Functions is given below:

1. A list contains elements of the same type arranged in sequential order and following operations can be performed on the list.

• get() — Return an element from the list at any given position.
• insert() — Insert an element at any position of the list.
• remove() — Remove the first occurrence of any element from a non-empty list.
• removeAt() — Remove the element at a specified location from a non-empty list.
• replace() — Replace an element at any position by another element.
• size() — Return the number of elements in the list.
• isEmpty() — Return true if the list is empty, otherwise return false.
• isFull() — Return true if the list is full, otherwise return false.
• Stack ADT
• In Stack ADT Implementation instead of data being stored in each node, the pointer to data is stored.
• The program allocates memory for the data and address is passed to the stack ADT.

• The head node and the data nodes are encapsulated in the ADT. The calling function can only see the pointer to the stack.
• The stack head structure also contains a pointer to top and count of number of entries currently in stack.

1. A Stack contains elements of the same type arranged in sequential order. All operations take place at a single end that is top of the stack and following operations can be performed:

• push() — Insert an element at one end of the stack called top.
• pop() — Remove and return the element at the top of the stack, if it is not empty.
• peek() — Return the element at the top of the stack without removing it, if the stack is not empty.
• size() — Return the number of elements in the stack.
• isEmpty() — Return true if the stack is empty, otherwise return false.
• isFull() — Return true if the stack is full, otherwise return false.

1. Queue ADT

• The queue abstract data type (ADT) follows the basic design of the stack abstract data type.

Each node contains a void pointer to the data and the link pointer to the next element in the queue. The program’s responsibility is to allocate memory for storing the data.

A Queue contains elements of the same type arranged in sequential order. Operations take place at both ends, insertion is done at the end and deletion is done at the front. Following operations can be performed:

• enqueue() — Insert an element at the end of the queue.
• dequeue() — Remove and return the first element of the queue, if the queue is not empty.
• peek() — Return the element of the queue without removing it, if the queue is not empty.
• size() — Return the number of elements in the queue.
• isEmpty() — Return true if the queue is empty, otherwise return false.
• isFull() — Return true if the queue is full, otherwise return false.

Arrays:-

Java provides a data structure, the array, which stores a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type.

Instead of declaring individual variables, such as number0, number1, …, and number99, you declare one array variable such as numbers and use numbers[0], numbers[1], and …, numbers[99] to represent individual variables.

Declaring Array Variables

To use an array in a program, you must declare a variable to reference the array, and you must specify the type of array the variable can reference. Here is the syntax for declaring an array variable −

Syntax

dataType[] arrayRefVar;   // preferred way.
or
dataType arrayRefVar[];  // works but not preferred way.
Creating Arrays

You can create an array by using the new operator with the following syntax −

Syntax

arrayRefVar = new dataType[arraySize];

The above statement does two things −

• It creates an array using new dataType[arraySize].
• It assigns the reference of the newly created array to the variable arrayRefVar.

Declaring an array variable, creating an array, and assigning the reference of the array to the variable can be combined in one statement, as shown below −

dataType[] arrayRefVar = new dataType[arraySize];

Alternatively you can create arrays as follows −

dataType[] arrayRefVar = {value0, value1, ..., valuek};.