Character.isJavaIdentifierStart() method in Java

The java.lang.Character.isJavaIdentifierStart(char ch) is an inbuilt method in java which determines if the specified character is permissible as the first character in a Java identifier or not. A character may start as a Java identifier if and only if one of the following conditions is true:

  • isLetter(ch) returns true
  • getType(ch) returns LETTER_NUMBER
  • ch is a currency symbol (such as ‘$’)
  • ch is a connecting punctuation character (such as ‘_’).

Note: This method cannot handle supplementary characters. To support all Unicode characters, including supplementary characters, use the isJavaIdentifierStart(int) method.

Syntax:



public static boolean isJavaIdentifierStart(char ch)

Parameters: The function accepts one mandatory parameter ch which specifies the character to be tested.

Return value: This method returns a boolean value. The boolean value is True if the character may start a Java identifier, False otherwise.

Program below demonstrates the Character.isJavaIdentifierStart(char ch) method:

Program 1:

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// Java program to demonstrate the
// Character.isJavaIdentifierStart()
import java.lang.*;
  
public class gfg {
  
    public static void main(String[] args)
    {
  
        // create 2 char primitives c1, c2
        char c1 = '9', c2 = '-';
  
        // assign isJavaIdentifierStart results of c1, c2
        // to boolean primitives  bool1, bool2
        boolean bool1 = Character.isJavaIdentifierStart(c1);
        System.out.println(c1 + " may start a Java identifier is : " + bool1);
  
        boolean bool2 = Character.isJavaIdentifierStart(c2);
        System.out.println(c2 + " may start a Java identifier is : " + bool2);
    }
}

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Output:

9 may start a Java identifier is : false
- may start a Java identifier is : false

Program 2:

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// Java program to demonstrate the
// Character.isJavaIdentifierStart()
  
import java.lang.*;
  
public class gfg {
  
    public static void main(String[] args)
    {
  
        // create 2 char primitives c1, c2
        char c1 = '5', c2 = '_';
  
        // assign isJavaIdentifierStart results of c1, c2
        // to boolean primitives  bool1, bool2
        boolean bool1 = Character.isJavaIdentifierStart(c1);
        System.out.println(c1 + " may start a Java identifier is : " + bool1);
  
        boolean bool2 = Character.isJavaIdentifierStart(c2);
        System.out.println(c2 + " may start a Java identifier is : " + bool2);
    }
}

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Output:

5 may start a Java identifier is : false
_ may start a Java identifier is : true

Reference: https://docs.oracle.com/javase/7/docs/api/java/lang/Character.html#isJavaIdentifierStart(char)



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