Infix to Postfix Conversion (Application of Stacks and Queues: Expression Parsing)

Write a program, In2pJ, which reads in an infix expression from the console and outputs a

postfix expression that can subsequently be processed by a simple interpreter. This output will

be used in the next assignment to create a simple 4-function calculator, as outlined in the

attached file. You are not being asked to do a full implementation of the calculator, only the first

stage which converts an algebraic expression of the form 34 / 5 + 16 * 2 (infix) to postfix

notation, which for this example is 34 5 / 16 2 * +.

Note that in the above example, the program is run in an infinite loop – you do not need to do

this for the assignment. Expressions will be limited to operands, binary operators, and

parentheses only.


You are to use the Shunting Yard algorithm, the simple version of which is described in the

attached file, and uses 3 data structures: 2 queues for holding input and output and a stack for

holding operators. You have already seen the Stack class in Assignment 2. One of the

difficulties in writing this program is in parsing the input string and separating it into operators

and operands. The example below shows how the StrongTokenizer class for this purpose.

import [login to view URL];

import [login to view URL];

public class TestParse extends ConsoleProgram {

public void run() {

String str = readLine("Enter string: ");

StringTokenizer st = new StringTokenizer(str,"+-*/",true);

while ([login to view URL]()) {

println("-->"+[login to view URL]());




Here’s what happens when you run the program:

Enter string: 34/5+16*2








You need to devise an appropriate loop (hint, look at the while loop in the above example) that

enqueues this data in the input queue. From here, implementation of the Shunting Yard program

follows the recipe outlined in the attached description. Once your program is working, run

through each of the following test cases, saving the results to a file.

Test Cases:

Enter string (blank line to exit): 34/5+16*2

Postfix: 34 5 / 16 2 * +

Enter string (blank line to exit): 5+9.27/1.4*3 + 2/3

Postfix: 5 9.27 1.4 / 3 * + 2 3 / +

Enter string (blank line to exit): 1.1-2.2*3.4/5.6

Postfix: 1.1 2.2 3.4 * 5.6 / -

Enter string (blank line to exit): (3+4*5)*(6*(9-5))

Postfix: 3 4 5 * + 6 9 5 - * *

Enter string (blank line to exit): 1.4*(2.3-5.6)/(6.2-4.1)

Postfix: 1.4 2.3 5.6 - * 6.2 4.1 - /


Write the In2pJ program as described in the preceding sections. It should operate interactively

and be able to replicate the output from the test cases shown above. To obtain full marks your

code must be fully documented and correctly replicate the test cases.

Your submission should consist of 5 files:

1. [login to view URL] - stack class

2. [login to view URL] - queue class

3. [login to view URL] - node object

4. [login to view URL] - program

5. [login to view URL] - output

Квалификация: Java

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( 0 отзыв(-а, -ов) ) Montreal, Canada

ID проекта: #24106121