Jakarta Commons Cookbook

2.11. Testing the Contents of a String

Problem

You need to make sure a string contains only numbers, letters, or a combination of both.

Solution

Use the various StringUtils methods to validate user input; isNumeric( ) , isAlpha() , isAlphanumeric() , and isAlphaSpace() verify that a string does not contain any undesired characters:

String state = "Virginia"

System.our.println( "Is state number? " + 
                    StringUtils.isNumeric( state ) );
System.our.println( "Is state alpha? " + 
                    StringUtils.isAlpha( state ) );
System.our.println( "Is state alphanumeric? " + 
                    StringUtils.isAlphanumeric( state ) );
System.our.println( "Is state alphaspace? " + 
                    StringUtils.isAlphaspace( state ) );

This code tests the string “Virginia” against four validation methods, producing the following output:

Is state a number? false
Is state alpha? true
Is state alphanumeric? true
Is state alphaspace? true

Discussion

StringUtils.isNumeric( ) returns true if the string being tested contains only digits from 0 to 9. If you are asking a user to input a numerical value, such as year or age, you need to have a way to ensure that the input supplied is, in fact, a numeric value:

String test1 = "1976";
String test2 = "Mozart";

boolean t1val = StringUtils.isNumeric( test1 );
boolean t2val = StringUtils.isNumeric( test2 ); 

System.out.println( "Is " + test1 + " a number? " + t1val );
System.out.println( "Is " + test2 + " a number? " + t2val );

This code tests two strings and produces the following output:

Is 1976 a number? true ...