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Determine if a String is a legal Java Identifier
To determine if a String is a legal Java Identifier, use the Character.isJavaIdentifierPart() and Character.isJavaIdentifierStart() methods.
Character.isJavaIdentifierPart()
The java.lang.Character.isJavaIdentifierPart() determines if the character (Unicode code point) may be part of a Java identifier as other than the first character.
A character may be part of a Java identifier if any of the following are true.
- it is a letter
- it is a currency symbol (such as '$')
- it is a connecting punctuation character (such as '_')
- it is a digit
- it is a numeric letter (such as a Roman numeral character)
Character.isJavaIdentifierStart()
The java.lang.Character.isJavaIdentifierStart() determines if the character (Unicode code point) is permissible as the first character in a Java identifier.
A character may start a Java identifier if and only if one of the following conditions is true.
- isLetter(ch) returns true
- getType(ch) returns LETTER_NUMBER
- the referenced character is a currency symbol (such as '$')
- the referenced character is a connecting punctuation character (such as '_').
The following is an example that checks for individual characters in a string as well as an entire string. It checks whether the string can be a legal Java Identifier or not.
Example
import java.util.*;
public class Demo {
public static void main(String []args) {
char ch1, ch2;
ch1 = 's';
ch2 = '_';
String str = "jkv_yu";
System.out.println("Checking characters for valid identifier status...");
boolean bool1, bool2;
bool1 = Character.isJavaIdentifierPart(ch1);
bool2 = Character.isJavaIdentifierStart(ch2);
String str1 = ch1 + " may be a part of Java identifier = " + bool2;
String str2 = ch2 + " may start a Java identifier = " + bool2;
System.out.println(str1);
System.out.println(str2);
System.out.println("
Checking an entire string for valid identifier status...");
System.out.println("The string to be checked: "+str);
if (str.length() == 0 || !Character.isJavaIdentifierStart(str.charAt(0))) {
System.out.println("Not a valid Java Identifier");
}
for (int i = 1; i < str.length(); i++) {
if (!Character.isJavaIdentifierPart(str.charAt(i))) {
System.out.println("Not a valid Java Identifier");
}
}
System.out.println("Valid Java Identifier");
}
}Output
Checking characters for valid identifier status... s may be a part of Java identifier = true _ may start a Java identifier = true Checking an entire string for valid identifier status... The string to be checked: jkv_yu Valid Java Identifier
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