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    <p>Okay so after all the great advise from the guys I created a method that will take an input such as <code>-1+2(4+(2*(-2--1)))*-1.5</code> and split it to an array, such as <code>[-1, +, 2, (, 4, +, (, 2, *, (, -2, -, -1, ), ), ), *, -1.5]</code>.</p> <p>The way the method works is that it splits the input String using regex. With regex I was able to split all the numbers and operators. While this is great it wasn't able to handle negative values. Using regex it would always see <code>-</code> as a binary operator. I needed it to see it as a unary operator so that it could understand that it's a negative value. So what I did was compare each operator with the string that followed it. If this was also an operator I knew that the second one was a unary operator. I then also had to put in an if statement for if the first value was a <code>-</code> and if it was I knew that that was a unary operator.</p> <p>Here's the code so far. I'm sure there is an easier way to do this using a parser, I just couldn't wrap my head around it.</p> <pre><code>import java.util.ArrayList; import java.util.Arrays; public class expSplit { public String[] splitExp(String theexp){ ArrayList&lt;String&gt; tokens = new ArrayList&lt;String&gt;(); //System.out.println(theexp); String expression = theexp.replaceAll("\\s+", ""); //System.out.println(expression); String tem[] = expression.split("(?&lt;=[-+*/%(),])(?=.)|(?&lt;=.)(?=[-+*/%(),])"); ArrayList&lt;String&gt; temp = new ArrayList&lt;String&gt;(Arrays.asList(tem)); String orig = null; String regex = "[-+/%*]+"; String first = temp.get(0); tokens.add(first); String secound = temp.get(1); if(first.equals("-")){ tokens.remove(0); tokens.add(first+secound); } for (int i = 0; i &lt; temp.size(); i++) { String a = temp.get(i); if (i &gt;= 1){ String b = temp.get(i-1); if(b.matches(regex) &amp;&amp; a.matches("[-+]+")){ String c = temp.get(i-2); if(c.matches("[-+]+")){ //System.out.println("MATCH"); break; }else{ //System.out.println("NO MATCH"); orig = a; } }else if(orig != null &amp;&amp; orig.equals("-")){ tokens.add(orig + a); orig = null; }else{ tokens.add(a); } } } if(first.equals("+")){ tokens.remove(0); } if(first.equals("-")){ tokens.remove(1); } String[]tokenArray = new String[tokens.size()]; tokenArray = tokens.toArray(tokenArray); //System.out.print(tokens); return tokenArray; } } </code></pre> <p>Thanks for the help, Ciaran</p>
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