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POJava IndexOutOfBoundsException Error
 

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    <p>I realize that this may be and is probably a really dumb question but bare with me, I'm a newbie. Anyway, I'm trying to read a math expression like 3+9-2*10/5 from JOptionPane and get its result -- taking into account order of operations, of course. I split up the string into just digits and just operands using String.split() and created a for loop that is looking for either multiplication signs or division signs -- in this case it is detecting the string "*" since it comes up first in the string.</p> <pre><code>public static void main(String[] args) { String mathString = JOptionPane.showInputDialog("Please type a simple math expression (i.e., without parentheses)."); String[] parsedIntegers = mathString.split("\\D"); String[] parsedOperands = mathString.split("\\d+"); parsedOperands[0] = null; System.out.println(Arrays.toString(parsedIntegers)); System.out.println(Arrays.toString(parsedOperands)); for (int index = 1; index &lt;= parsedOperands.length; index = index + 1) { if (parsedOperands[index].equals("*")) { System.out.println("The multiplication sign is at index " + index + "."); int multResult = Character.getNumericValue(parsedIntegers[index - 1].charAt(index - 1)) * Character.getNumericValue(parsedIntegers[index].charAt(index)); System.out.println(multResult); } } } </code></pre> <p>The string array parsedOperands looks like this: [null, +, -, *, /]. The string array parsedIntegers looks like this: [3, 9, 2, 10, 5].</p> <p>However, when I look for "*" which is at index 3 in parsedOperands and then try to multiply what is in (index - 1) and (index) in parsedIntegers, Java returns an IndexOutOfBoundsException. Why does this happen? Am I missing something?</p> <p>Here is the error:</p> <pre><code>[3, 9, 2, 10, 5] Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 2 [null, +, -, *, /] The multiplication sign is at index 3. at java.lang.String.charAt(String.java:658) at programmingpractice.SolveMathExpression.main(SolveMathExpression.java:49) Java Result: 1 </code></pre>
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