validate mathematical variables expression in java -

which way validate mathematical variables expression. whether can use stack or regex expression.

i have gone http://www.sanfoundry.com/java-program-implement-evaluate-expression-using-stacks/

note: expression not contain parenthesis. example:

valid:

• x+3-y/2
• x+y
• 2+4+e

invalid:

• x++4+8
• e-3r
• e+r34-

how validate above expressions?i need validate mathematic expression input provided user in java

if no parentheses (i.e. nesting expressions) allowed, validation done simple regex:

final pattern pattern = pattern.compile("([0-9]+|[a-z]+)([-+*/]([0-9]+|[a-zaz]+))*");  (string s : arrays.aslist("123", "x+3-y/2", "x+y", "2+4+e", "x++4+8", "e-3r", "e+r34-", "---x+3-y/2")) {     system.out.format("%5s %s\n", pattern.matcher(s).matches(), s); } 

the output is

 true 123  true x+3-y/2  true x+y  true 2+4+e false x++4+8 false e-3r false e+r34- false ---x+3-y/2