Java Character isJavaIdentifierstart() Method

The isJavaIdentifierStart(char ch) method of Character class determines whether the given(or specified) character is considered as the first character in a Java identifier or not.

A character may start a Java identifier if and only if any of the following conditions is true:

isLetter(ch) returns true.
getType(ch) returns LETTER_NUMBER.
The character ch is a currency symbol.
The character ch is a connecting punctuation character such as '_'.

Note: The above method cannot be used to handle supplementary characters. In order to support all the Unicode characters, including all the supplementary character, we can use the isJavaIdentifierStart(int) method.

Syntax

Parameter

ch: It is the character that needs to be tested.

Return Value

The isJavaIdentifierStart(char ch) method returns a Boolean value i.e. true if the given(or specified) character may start a particular Java identifier. Otherwise, the method returns false.

Example 1

public class JavaChracterisJavaIdentifierStartExample1 {
    public static void main(String[] args) {
      // Create three char primitives ch1, ch2 and ch3.
         char ch1, ch2, ch3;
      // Assign values to ch1, ch2 and ch3.
         ch1 = '1';
         ch2 = '5';
         ch3 = '_';
      // Create three boolean primitives b1, b2 and b3.
      boolean b1, b2, b3;
      // Assign result to b1, b2 and b3.
      b1 = Character.isJavaIdentifierStart(ch1);
      b2 = Character.isJavaIdentifierStart(ch2);
      b3 = Character.isJavaIdentifierStart(ch3);
      String str1 = " The first character may start a Java identifier: " + b1;
      String str2 = " The second character may start a Java identifier: " + b2;
      String str3 = " The third character may start a Java identifier: " + b3;
      // print b1, b2 values
      System.out.println( str1 );
      System.out.println( str2 );
      System.out.println( str3 );
   }
}

Output:

The first character may start a Java identifier: false
 The second character may start a Java identifier: false
 The third character may start a Java identifier: true

Example 2

public class JavaChracterisJavaIdentifierStartExample2 {
    public static void main(String[] args) {
      // Create three char primitives ch1, ch2 and ch3.
         char ch1, ch2, ch3;
      // Assign values to ch1, ch2 and ch3.
         ch1 = 'A';
         ch2 = 'b';
         ch3 = 'G';
      // Create three boolean primitives b1, b2 and b3.
      boolean b1, b2, b3;
      // Assign result to b1, b2 and b3.
      b1 = Character.isJavaIdentifierStart(ch1);
      b2 = Character.isJavaIdentifierStart(ch2);
      b3 = Character.isJavaIdentifierStart(ch3);
      String str1 = " The first character may start a Java identifier: " + b1;
      String str2 = " The second character may start a Java identifier: " + b2;
      String str3 = " The third character may start a Java identifier: " + b3;
      // print b1, b2 values
      System.out.println( str1 );
      System.out.println( str2 );
      System.out.println( str3 );
   }
}

Output:

The first character may start a Java identifier: true
The second character may start a Java identifier: true
The third character may start a Java identifier: true

Example 3

import java.util.Scanner;
public class JavaChracterisJavaIdentifierStartExample3 {
    public static void main(String[] args) {
       // Ask the user to enter ther input.
	  System.out.print("Enter the first character:");
      // Use the Scanner class to get the user input
	 Scanner s1 = new Scanner(System.in);
      // Get a single character.
	 char value1 = s1.nextLine().toCharArray()[0];
      // Check the user input. 
	 boolean check1 = Character.isJavaIdentifierStart(value1);
     // print result
	 if (check1) {
System.out.print("The first input \'" + value1 + "\' may start a Java identifier.\n");
	} else {
System.out.print("The first input \'" + value1 + "\' may not start a Java identifier.\n");
		}
         System.out.print("Enter the second character:");
	 Scanner s2 = new Scanner(System.in);
	 char value2 = s2.nextLine().toCharArray()[0];
	 boolean check2 = Character.isJavaIdentifierStart(value1);
   
	 if (check2) {
System.out.print("The second input \'" + value2 + "\' may start a Java identifier.\n");
	} else {
System.out.print("The second input \'" + value2 + "\' may not start a Java identifier.\n");
		}
	}
}

Output:

Enter the first character:)
The first input ')' may not start a Java identifier.
Enter the second character:k
The second input 'k' may not start a Java identifier.

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