Stack In JAVA

[scurged09]

Stack in JAVA

In this tutorial you will learn
1) What is a stack?
2) How is stack used in programming?
3) Implementation of stack in JAVA
What is a stack?
Stack is one of the most important data structure in programming, it can be imagined as the bottle of balls which is open from one end. So the addition and deletion of balls can be done through one end only. The element which goes last in the stack is first to be extracted from the stack. So the stack works on last in first out principle (LIFO).
How is stack used in programming
Stack is very useful for programming purposes. The stack can be used to store the last used values of some variables as well as in operating system and micro controller programming the stacks can be used handle interrupts and used to store the program counter values and addresses.

Implementation of stack in JAVA
The stack in JAVA is implemented using ordinary array. Stack has few functions associated with it. They are:
Push: Used to put data into the stack
Pop: Used to remove data from the top of the stack
Top: The first element of the array is called the top of the stack.
In the code below first I have defined the class Stack, this class contains data members, methods and the constructor which initialize the data members. Then in the main of the program I have the object of stack class and performed operations on it using its methods. The detail and significance of each line is provided in the comments with the code below.

1. import
   
   java.util.Scanner
   
   ;
   
2. 
   
3. 
   
4. public
   
   class
   
   UsingJAVA {
   
5. public
   
   static
   
   class
   
   Stack
   
   {
   
   //we are defining the stack class
   
6. private
   
   int
   
   maximumSize;
   
   //its the size of the array
   
7. private
   
   int
   
   [
   
   ]
   
   structure;
   
   //this is the array in which the contents are stored
   
8. private
   
   int
   
   top;
   
9. public
   
   Stack
   
   (
   
   int
   
   M)
   
   //this is the constructor
   
10. {
    
11. maximumSize =
    
    M;
    
    //The size of the array is of the user's choice
    
12. structure =
    
    new
    
    int
    
    [
    
    maximumSize]
    
    ;
    
    // we are making an array
    
13. top =
    
    -
    
    1
    
    ;
    
    // top is declared -1 because we need to access the 0th postion at first insertion
    
14. }
    
15. public
    
    void
    
    push(
    
    int
    
    j)
    
    //function to put values into stack.
    
16. {
    
17. structure[
    
    ++
    
    top]
    
    =
    
    j;
    
    //the value of top pointer is increased and value is inserted
    
18. }
    
19. public
    
    int
    
    pop(
    
    )
    
    //to take data out of the stack
    
20. {
    
21. return
    
    structure[
    
    top--
    
    ]
    
    ;
    
    //decrement takes the top to the element below the top element
    
22. }
    
23. 
    
24. public
    
    boolean
    
    isEmpty(
    
    )
    
    //standard function to check whether the stack is empty or not
    
25. {
    
26. return
    
    (
    
    top ==
    
    -
    
    1
    
    )
    
    ;
    
27. }
    
28. public
    
    boolean
    
    isFull(
    
    )
    
    //standard function to check if the stack is full?
    
29. {
    
30. return
    
    (
    
    top ==
    
    maximumSize -
    
    1
    
    )
    
    ;
    
31. }
    
32. public
    
    static
    
    void
    
    main(
    
    String
    
    [
    
    ]
    
    args)
    
    {
    
33. int
    
    x;
    
34. System
    
    .out
    
    .println
    
    (
    
    "What should be the size of the stack?"
    
    )
    
    ;
    
35. Scanner inputScanner=
    
    new
    
    Scanner(
    
    System
    
    .in
    
    )
    
    ;
    
36. x=
    
    inputScanner.nextInt
    
    (
    
    )
    
    ;
    
37. Stack
    
    Workstack =
    
    new
    
    Stack
    
    (
    
    x)
    
    ;
    
    //the object of the stack class is made
    
38. System
    
    .out
    
    .println
    
    (
    
    "Please enter the values you want to insert into stack"
    
    )
    
    ;
    
39. for
    
    (
    
    int
    
    j=
    
    0
    
    ;
    
    j<
    
    x ;
    
    j++
    
    )
    
    //for loop used to insert the number of values into the stack
    
40. {
    
    int
    
    z;
    
41. z=
    
    inputScanner.nextInt
    
    (
    
    )
    
    ;
    
42. Workstack.push
    
    (
    
    z)
    
    ;
    
    //pushing a value into stack
    
43. }
    
44. System
    
    .out
    
    .println
    
    (
    
    "The contents of the stack are popped out and they are:"
    
    )
    
    ;
    
45. while
    
    (
    
    !
    
    Workstack.isEmpty
    
    (
    
    )
    
    )
    
    {
    
46. int
    
    element =
    
    Workstack.pop
    
    (
    
    )
    
    ;
    
    //retrieving each element and saving it in variable
    
47. System
    
    .out
    
    .print
    
    (
    
    element)
    
    ;
    
    //displaying the variable to screen.
    
48. System
    
    .out
    
    .println
    
    (
    
    )
    
    ;
    
49. }
    
50. System
    
    .out
    
    .println
    
    (
    
    )
    
    ;
    
51. }
    
52. }
    
53. 
    
54. }
    

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