Determine if a string is a valid Java identifier

To determine if a String is a valid Java identifier, use the Character.isJavaIdentifierPart() and Character.isJavaIdentifierStart() methods.

Character.isJavaIdentifierPart()

java.lang.Character.isJavaIdentifierPart() determines whether the character (Unicode code point) can be part of a Java identifier, not the first character.

If any of the following conditions are met, the character may be part of a Java identifier.

• It is a letter

• It is a currency symbol (e.g., "$")

• It is a connected punctuation symbol (e.g., '_')

• It is a numeral

• It is a numeral-letter (e.g., Roman numeral characters)

Character.isJavaIdentifierStart()

java.lang.Character.isJavaIdentifierStart() determines whether the character (Unicode code point) is allowed as the first character in a Java identifier.

and only when one of the following conditions is true, the character can start a Java identifier.

• isLetter(ch) returns true

• getType(ch) returns LETTER_NUMBER

• The referenced character is a currency symbol (e.g., "$").

• The referenced character is a connected punctuation character (e.g., "_").

This is an example of checking a single character within a string and the entire string. It checks if the string can be a valid Java identifier.

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("\nChecking 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 Result

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