Due Date: Monday, February 14, 2022.

Please complete Lab 3 before you start working on the homework. In this homework, you will continue the work on the project started in the lab and implement a balance checker for parentheses, braces, and square brackets in a string.

a. Static Attributes.

In the Interface class, add two static attributes of type String called openSym and closedSym and initialize them as "([{<" and ")]}>" respectively. These will be used to identify open and closed elements in the string. It's important that the closing symbols be placed at the same index as the matching open ones.

b. Balance Function.

Add a function in the interface called balanceCheck that receives a string as parameter and that checks if the open and closed symbols that are stored in the two attributes defined at point a) above are well balanced. The function should return an integer with the value

• 0 if the string is well balanced,
• 1 if there are some unmatched open symbols by the end of the process, and
• -1 if there is at least one closing symbol that doesn't match the latest still open symbol when you process it.

The function should not output anything, just return the result.

To check if the string is balanced, declare a stack at the beginning of the function. Then you need a loop that goes through the string and looks at every character one by one. For each of them,

• check if that character can be found in openSym, and if yes, then push it onto the stack. You can use the string function contains for this part.
• If not, check if the character can be found in closedSym.
• If yes, then get its index in this string. You can use the string function indexOf for this part. Then get the character in the string openSym at the same index.
• If the stack character matches the one from openSym from the index, then pop the open character from the stack.
• If they don't match, then return -1. The rest of the string doesn't need to be processed.
• If the current character is neither in openSym, nor in closedSym, then you can just ignore it.

At the end of the loop, if the stack is empty, then return 0. Otherwise return 1.

c. Main.

In the main, comment out the call to testStack from the lab. Then declare an input string and ask the user to input it. You will need a scanner for this, and you can use either the function next, or nextLine. Then call the function balanceCheck to check if the string is well balanced, and output an appropriate message based on what value the function returns. Make sure not to call the function more than once even when checking for multiple values - hint: use a local variable to store the result. After that, ask the user if they want to test another string, and repeat the process until the user quits. You can handle the last part however you choose.

d. Test.

Here are some strings that you can test:

• "((a{bd}cu)o)" : is a well balanced string;
• "[[[(()[()])]]{<>}]" : is another well balanced string;
• "((()])" contains a closing symbol (']') that doesn't match the latest still open symbol;
• "[[((){{}})" : is a string that contains some open symbols that are unmatched by the end of it.

Upload all four .java files to Canvas, Assignments, Homework 5.