Java Program to Implement Shunting Yard Algorithm

This is a Java Program to Implement Shunting Yard Algorithm. Shunting Yard algorithm is used for converting an infix expression into a postfix expression.

Here is the source code of the Java Program to Implement Shunting Yard Algorithm. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

  1. /**
  2.  ** Java Program to Implement Shunting Yard Algorithm
  3.  **/
  4.  
  5. import java.util.Scanner;
  6.  
  7. /** Class ShuntingYard **/
  8. public class ShuntingYard
  9. {
  10.     /** enum **/
  11.     private enum Precedence
  12.     {
  13.         lparen(0), rparen(1), plus(2), minus(3), divide(4), times(5), mod(6), eos(7), operand(8);
  14.  
  15.         private int index;
  16.         Precedence(int index)
  17.         {
  18.             this.index = index;
  19.         }
  20.         public int getIndex()
  21.         {
  22.             return index;
  23.         }        
  24.     } 
  25.     /** in stack precedence **/
  26.     private static final int[] isp = {0, 19, 12, 12, 13, 13, 13, 0};
  27.     /** incoming character precedence **/
  28.     private static final int[] icp = {20, 19, 12, 12, 13, 13, 13, 0};
  29.     /** operators **/
  30.     private static final char[] operators = {'{', '}', '+', '-', '/', '*', '%', ' '};
  31.     /** precedence stack **/
  32.     private Precedence[] stack; 
  33.     /** stack top pointer **/
  34.     private int top;
  35.  
  36.     /** pop element from stack **/
  37.     private Precedence pop()
  38.     {
  39.         return stack[top--];
  40.     }
  41.     /** push element onto stack **/
  42.     private void push(Precedence ele)
  43.     {
  44.         stack[++top] = ele;
  45.     }
  46.     /** get precedence token for symbol **/
  47.     public Precedence getToken(char symbol)
  48.     {
  49.         switch (symbol)
  50.         {
  51.         case '('  : return Precedence.lparen;
  52.         case ')'  : return Precedence.rparen;
  53.         case '+'  : return Precedence.plus;
  54.         case '-'  : return Precedence.minus;
  55.         case '/'  : return Precedence.divide;
  56.         case '*'  : return Precedence.times;
  57.         case '%'  : return Precedence.mod;
  58.         case ' '  : return Precedence.eos;
  59.         default   : return Precedence.operand;
  60.         }
  61.     }
  62.  
  63.     /** Function to convert infix to postfix **/
  64.     public String postfix(String infix)
  65.     {
  66.         String postfix = "";
  67.         top = 0;
  68.         stack = new Precedence[infix.length()];
  69.         stack[0] = Precedence.eos;
  70.         Precedence token;
  71.         for (int i = 0; i < infix.length(); i++)
  72.         {
  73.             token = getToken(infix.charAt(i));
  74.             /** if token is operand append to postfix **/
  75.             if (token == Precedence.operand)
  76.                 postfix = postfix + infix.charAt(i);
  77.             /** if token is right parenthesis pop till matching left parenthesis **/
  78.             else if (token == Precedence.rparen)
  79.             {
  80.                 while (stack[top] != Precedence.lparen)
  81.                     postfix = postfix + operators[pop().getIndex()];
  82.                 /** discard left parenthesis **/
  83.                 pop();
  84.             }
  85.             /** else pop stack elements whose precedence is greater than that of token **/
  86.             else
  87.             {
  88.                 while (isp[stack[top].getIndex()] >= icp[token.getIndex()])
  89.                     postfix = postfix + operators[pop().getIndex()];
  90.                 push(token);
  91.             }
  92.         }
  93.         /** pop any remaining elements in stack **/
  94.         while ((token = pop()) != Precedence.eos)
  95.             postfix = postfix + operators[token.getIndex()];
  96.  
  97.         return postfix;
  98.     }
  99.     /** Main function **/
  100.     public static void main (String[] args) 
  101.     {
  102.         Scanner scan = new Scanner(System.in);
  103.         System.out.println("Shunting Yard Algorithm Test\n");
  104.         /** Make an object of ShuntingYard class **/
  105.         ShuntingYard sy = new ShuntingYard();
  106.  
  107.         /** Accept infix expression **/
  108.         System.out.println("Enter infix expression");
  109.         String infix = scan.next();
  110.  
  111.         String postfix = sy.postfix(infix);
  112.         System.out.println("\nPostfix expression : "+ postfix);
  113.     }
  114. }


Shunting Yard Algorithm Test
 
Enter infix expression
1+2*3/4-5%6*7/8+9-1
 
Postfix expression : 123*4/+56%7*8/-9+1-

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Manish Bhojasia, a technology veteran with 17+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer and SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage & Cluster Administration, Advanced C Programming, SAN Storage Technologies, SCSI Internals and Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him below.


Sanfoundry Training Center of Excellence (CoE)

Manish Bhojasia, a technology veteran with 17+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer and SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage & Cluster Administration, Advanced C Programming, SAN Storage Technologies, SCSI Internals and Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him below.







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