String split method

[DavidG24]

Hi guys,

I'm trying to write a method to convert a mathematical expression into a function using Java

I'm starting with really basic functions, i.e.

x^2 + x + 2

now as a starting point, I'm hoping to split the String i.e.

"x^2 + x + 2"

using the split method of the String class, now given I was to split using the addition symbols I thought I would use

"x^2 + x + 2".split("+");

however this produces the following error (using Netbeans)

Exception in thread "main" java.util.regex.PatternSyntaxException: Dangling meta character '+' near index 0
+
^
at java.util.regex.Pattern.error(Pattern.java:1713)
at java.util.regex.Pattern.sequence(Pattern.java:1878 )
at java.util.regex.Pattern.expr(Pattern.java:1752)
at java.util.regex.Pattern.compile(Pattern.java:1460)
at java.util.regex.Pattern.<init>(Pattern.java:1133)
at java.util.regex.Pattern.compile(Pattern.java:823)
at java.lang.String.split(String.java:2292)
at java.lang.String.split(String.java:2334)
at functionbuilder.Main.main(Main.java:19)
Java Result: 1


Was just wondering if this can be overcome with the split method?

Thanks in Advance,

Cheers,

David

[KevinWorkman]

Check out the Pattern API to figure out how to use regular expressions.

Pattern (Java Platform SE 6)

[DavidG24]

Hi Kevin,

Thanks for linking that, Sorry I'm fairly new to Java and am still puzzled by this :-(
When I try
Pattern p = Pattern.compile("+")
I get a similar error as before, I'm sure I'm missing something simple - any further suggestions would be greatly appreciated.

Cheers,

David

[JosAH]

When I try
Pattern p = Pattern.compile("+")
I get a similar error as before, I'm sure I'm missing something simple - any further suggestions would be greatly appreciated.

The '+' character has a special meaning in regular expressions: it's the transitive closure of a regular expression: 'one or more times'. You have to escape it to make it an ordinary character: "\\+".

kind regards,

Jos

[KevinWorkman]

Uh, yeah. That error would be expected. What does the API say about using a "+" symbol? What does it say about escaping literals?

Edit- Jos made it easy for you. :p

[DavidG24]

Hi JosAH,

cheers for that mate! working now :-)
And thanks again Kevin..

David