Java Programs[Important]

1.  
2.   WRITE A JAVA PROGRAM that: (a) (b) (c) Implements a Stack ADT Converts Infix expression to Postfix expression Evaluates a Postfix expression
3.  
4. Program :
5.  
6. import   .io.*;
7.  
8. interface stack { void push(int item); int pop(); }
9. class Stackimpl { private int stck[]; private int top;   
10. 
    
11. Stackimpl(int size) { stck=new int[size]; top=-1; }
12.  
13. void push(int item) { if(top==stck.length-1) System.out.println("stack is full insertion is not possible");
14.  
15. else stck[++top]=item; }
16.  
17. int pop() { if(top==-1) {
18.  
19. System.out.println("stack is empty deletion is not possible"); return 0; } else return stck[top--]; } }
20.  
21. class Stackdemo {
22.  
23. public static void main(String args[])throws IOException { int a[];
24.  
25. BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
26.  
27. System.out.println("enter the size of the array"); int n=Integer.parseInt(br.readLine());
28.  
29. Stackimpl obj1=new Stackimpl(n);
30.  
31. a=new int[n];
32.  
33. System.out.println("enter numbers into the stack");
34.  
35. for(int i=0;i<n;i++) a[i]=Integer.parseInt(br.readLine());
36.  
37. System.out.println("numbers are inserted"); for(int i=0;i<n;i++) obj1.push(a[i]);
38.  
39. System.out.println("The following numbers are poped out."); for(int i=0;i<n;i++) System.out.println(" "+obj1.pop());
40.  
41. } }