How to print results to screen

[NinjaLink]

First I want to say that I am a Java beginner and this is my 2nd program.

I created a program that will do a symbol balance test, but I need someone to help me print the results to the screen because I am getting a blank output whenever I try to find a way to do it. I am also reading into a file. Any help is appreciated please.

test.txt looks like {{}}

For ex,

{ { } } = the symbols are equally balanced
{ [ { } = the symbols are not equally balanced

I need someone to help me find a way to print the results like

{{}} are equally balanced
or
{[}} are not equally balanced


I tried using this and placing it near the bottom of the program in between the last brackets

while (!s.empty())
{
System.out.println(s.pop());
if (failed == true)
{
System.out.println(" symbols do not match");
}
else
{
System.out.println(" The symbols match");
}

Main Program:

import java.io.* ;

public class Stackmain 
{

    public Stackmain() 
    {
    	
    	
    	
    }
    public static boolean main(String expression) throws IOException 
    {
    
    final char LEFT_PARENT = '(';
    final char RIGHT_PARENT = ')';
    final char LEFT_CURLY = '{';
    final char RIGHT_CURLY = '}';
    final char LEFT_SQUARE = '[';
    final char RIGHT_SQUARE = ']';
    
    Stack s = new Stack(100);
    char ch;
    int i = 0;
    boolean failed = false;
    
    FileInputStream fstream = new FileInputStream("test.txt");

    DataInputStream in = new DataInputStream(fstream);
        BufferedReader br = new BufferedReader(new InputStreamReader(in));
    String strLine;
  
    while ((ch = (char)br.read()) != (char)-1 )
       if (!s.full()) 
       {
         for (i=0; !failed && (i < expression.length( )); i++)
          {
       	     switch (expression.charAt(i))
       	     {
       		  case LEFT_PARENT:
       		  case LEFT_CURLY:
       		  case LEFT_SQUARE:
       		       s.push(expression.charAt(i));
       		       break;
       		  case RIGHT_PARENT:
       		 if (s.empty() || (s.pop() != LEFT_PARENT))
       			   failed = true;
       			   break;
       	  	  case RIGHT_CURLY:
       		 if (s.empty() || (s.pop() != LEFT_CURLY))
       			   failed = true;
       			   break;
       		  case RIGHT_SQUARE:
       		 if (s.empty() || (s.pop() != LEFT_SQUARE))
       			   failed = true;
       			   break;     			 	
         	} 	
          }
       	}
       	   return (s.empty() && !failed);
     }             
}

Stack Class

class Stack {
   private int maxStack;
   private int emptyStack;
   private int top;
   private char[] items;




   public Stack(int size) {
      maxStack= size;
      emptyStack = -1;
      top = emptyStack;
      items = new char[maxStack];
   }

   

   public void push(char c) {
      items[++top] = c;
   }

   public char pop() {
      return items[top--];
   }

   public boolean full()  {
      return top + 1 == maxStack;
   }

   public boolean empty()  {
      return top == emptyStack;
   }
}

[NinjaLink]

I still receive a blank screen when I try to print...

My latest modification to try to print is below:

import java.io.* ;

public class Stackmain 
{

   // public Stackmain() 
   // {
    	
    	
   // }
    public static boolean main(String expression) throws IOException 
    {
    
    final char LEFT_PARENT = '(';
    final char RIGHT_PARENT = ')';
    final char LEFT_CURLY = '{';
    final char RIGHT_CURLY = '}';
    final char LEFT_SQUARE = '[';
    final char RIGHT_SQUARE = ']';
    
    Stack s = new Stack(100);
    char ch;
    int i = 0;
    boolean failed = false;
    
    FileInputStream fstream = new FileInputStream("test.txt");

    DataInputStream in = new DataInputStream(fstream);
    BufferedReader br = new BufferedReader(new InputStreamReader(in));
 
  
  
    while ((ch = (char)br.read()) != (char)-1 )
    {
       if (!s.full()) 
       {

         for (i=0; !failed && (i < expression.length( )); i++)
          {
       	     switch (expression.charAt(i))
       	     {
       		  case LEFT_PARENT:
       		  case LEFT_CURLY:
       		  case LEFT_SQUARE:
       		       s.push(expression.charAt(i));	  
       		       break;
       		  case RIGHT_PARENT:
       		 if (s.empty() || (s.pop() != LEFT_PARENT))
       			   failed = true;
       			   break;
       	  	  case RIGHT_CURLY:
       		 if (s.empty() || (s.pop() != LEFT_CURLY))
       			   failed = true;
       			   break;
       		  case RIGHT_SQUARE:
       		 if (s.empty() || (s.pop() != LEFT_SQUARE))
       			   failed = true;
       			   break;    
       			   
       			   			 	
         	} 	

          }
     }
         
}


if (failed == true)
{
	System.out.println("Expression does not match");
}
if (failed == false)
{
	System.out.println("Expression does match");
}

return (s.empty() && !failed);
}
}

[keang]

You're getting a blank screen because you aren't running anything. To run your class you need a main method with this signature:

public static void main(String[] args)

Whilst looking at the code I also noticed

• You are reading in a file and then not doing anything with the character you've just read in.
• You are using a stack but never putting anything into it.
• A better way to write the print out is section is:
  

  if (failed)
  {
  	System.out.println("Expression does not match");
  }
  else
  {
  	System.out.println("Expression does match");
  }

[NinjaLink]

Thank you for the reply. I will look into it now. I appreciate it!

[NinjaLink]

3 errors:
cannot find symbol variable expression
cannot return a value from method whose result type is void
variable expression might not have been initialized


Question: When I deleted public static boolean main(String expression), I was using expression in my for loop before. Is there something that I can use to replace it?


Here is my latest code:

import java.io.* ;

class Stackmain 
{
    public static void main(String[] args) throws IOException 
    {
    
    final char LEFT_PARENT = '(';
    final char RIGHT_PARENT = ')';
    final char LEFT_CURLY = '{';
    final char RIGHT_CURLY = '}';
    final char LEFT_SQUARE = '[';
    final char RIGHT_SQUARE = ']';
    
    Stack s = new Stack(100);
    char ch;
   // String expression;
    int i = 0;
    boolean failed = false;
    
    FileInputStream fstream = new FileInputStream("test.txt");

    DataInputStream in = new DataInputStream(fstream);
    BufferedReader br = new BufferedReader(new InputStreamReader(in));
 
  
  
    while ((ch = (char)br.read()) != (char)-1 )
    {
       if (!s.full()) 
       {

         for (i=0; !failed && (i < expression.length( )); i++)
          {
       	     switch (expression.charAt(i))
       	     {
       		  case LEFT_PARENT:
       		  case LEFT_CURLY:
       		  case LEFT_SQUARE:
       		       s.push(expression.charAt(i));	  
       		       break;
       		  case RIGHT_PARENT:
       		 if (s.empty() || (s.pop() != LEFT_PARENT))
       			   failed = true;
       			   break;
       	  	  case RIGHT_CURLY:
       		 if (s.empty() || (s.pop() != LEFT_CURLY))
       			   failed = true;
       			   break;
       		  case RIGHT_SQUARE:
       		 if (s.empty() || (s.pop() != LEFT_SQUARE))
       			   failed = true;
       			   break;    
       			   
       			   			 	
         	} 	

          }
     }
         
}


if (failed == true)
{
	System.out.println("Expression does not match");
}
if (failed == false)
{
	System.out.println("Expression does match");
}

//return (s.empty() && !failed);
}
}

[keang]

I was using expression in my for loop before. Is there something that I can use to replace it?

public static void main(String[] args) throws IOException 
{
String expression = null;

if ( args.length > 0 )
    {
    expression = args[0];
    }

...