Please add the necessary code to ArrayStack.java (listed as "ADD CODE HERE"). The code for BalanceChecker.java and StackInterface.java is also provided for the whole program.

ArrayStack.java

import java.util.Arrays; import java.util.EmptyStackException;

public class ArrayStack implements StackInterface { private T[] entries; private int topIndex; // index of top entry private static final int DEFAULT_CAPACITY = 50; private static final int MAX_CAPACITY = 10000;

public ArrayStack() { this(DEFAULT_CAPACITY); }

public ArrayStack(int initialCapacity) { checkCapacity(initialCapacity);

@SuppressWarnings("unchecked") T[] tempStack = (T[])new Object[initialCapacity]; entries = tempStack; topIndex = -1; }

@Override public T pop() { if(isEmpty()) { throw new EmptyStackException(); } else { T top = entries[topIndex]; entries[topIndex] = null; topIndex--; return top; } }

@Override public void push(T newEntry) { ensureCapacity(); entries[topIndex + 1] = newEntry; topIndex ++; }

@Override public T peek() { if(isEmpty()) { throw new EmptyStackException(); } else { return entries[topIndex]; } }

@Override public boolean isEmpty() { // ADD CODE HERE return true; }

@Override public void clear() { // ADD CODE HERE }

private void ensureCapacity() { if(topIndex == entries.length - 1) { int newLength = 2 * entries.length; checkCapacity(newLength); entries = Arrays.copyOf(entries, newLength); } }

private void checkCapacity(int capacity) { if (capacity > MAX_CAPACITY) { throw new IllegalStateException("Capacity too large"); } } }

BalanceChecker.java

public class BalanceChecker { public static boolean checkBalance(String expression) { StackInterface openDelimiterStack = new ArrayStack<>(); int characterCount = expression.length(); boolean isBalanced = true; int index = 0; char nextCharacter = ' ';

while(isBalanced && (index < characterCount)) { nextCharacter = expression.charAt(index); switch (nextCharacter) { case '(': case '[': case '{': openDelimiterStack.push(nextCharacter); break; case ')': case ']': case '}': if(openDelimiterStack.isEmpty()) { isBalanced = false; } else { char openDelimiter = openDelimiterStack.pop(); isBalanced = isPaired(openDelimiter, nextCharacter); } break; default: break; } index ++; } if(!openDelimiterStack.isEmpty()) { isBalanced = false; } return isBalanced; }

private static boolean isPaired(char open, char close) { return (open == '(' && close == ')') || (open == '[' && close == ']') || (open == '{' && close == '}'); } }

StackInterface.java

import java.util.EmptyStackException;

public interface StackInterface { /** Adds a new entry to the top of this stack. * @param newEntry An object to be added to the stack. */ void push(T newEntry);

/** Removes and returns this stack's top entry * @return The object at the top of the stack * @throws EmptyStackException if the stack is empty*/ T pop();

/** Retrieves this stack's top entry. * @return The object at the top of the stack. * @throws EmptyStackException if the stack is empty.*/ T peek();

/** Detects whether this stack is empty * @return True if the stack is empty. */ boolean isEmpty();

/** removes all entries from this stack */ void clear(); }