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The Character.isJavaIdentifierStart(int codePoint) is an inbuilt method in java that determines if the character (Unicode code point) is permissible as the first character in a Java identifier. It is to be noted that 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
ch is a currency symbol (such as ‘$’)
ch is a connecting punctuation character (such as ‘_’).

Syntax:

public static boolean isJavaIdentifierStart(int codePoint)

Parameters: The parameter codePoint is of the integer type and refers to the character (Unicode code point) that is to be tested. Return value: The isJavaIdentifierStart(int codePoint) method of Character class returns true if the character may start a Java identifier; false otherwise. Below programs illustrate the Character.isJavaIdentifierStart() method: Program 1:

Java

// Java program to illustrate
// Character.isJavaIdentifierStart() method 
import java.lang.*;

public class gfg {

    public static void main(String[] args)
    {

        // Create 2 int primitives c1, c2
        int c1 = 0x0039, c2 = 0x004b, c3 = 0x0081;

        // Assign isJavaIdentifierPart results of 
        // c1, c2 to boolean primitives bool1, bool2

        boolean bool1 = Character.isJavaIdentifierStart(c1);
        boolean bool2 = Character.isJavaIdentifierStart(c2);
        boolean bool3 = Character.isJavaIdentifierStart(c3);

        String str1 = "c1 may start a Java identifier is " + bool1;
        String str2 = "c2 may start a Java identifier is " + bool2;
        String str3 = "c3 may start a Java identifier is " + bool3;

        // Print bool1, bool2 values
        System.out.println(str1);
        System.out.println(str2);
        System.out.println(str3);
    }
}

Output:

c1 may start a Java identifier is false
c2 may start a Java identifier is true
c3 may start a Java identifier is false

Program 2:

Java

// Java program to illustrate
// Character.isJavaIdentifierStart() method 
import java.lang.*;

public class gfg {

    public static void main(String[] args)
    {

        // Create 2 int primitives c1, c2
        int c1 = 0x0034, c2 = 0x005a;

        // Assign isJavaIdentifierPart results of 
        // c1, c2 to boolean primitives bool1, bool2

        boolean bool1 = Character.isJavaIdentifierStart(c1);
        boolean bool2 = Character.isJavaIdentifierStart(c2);

        String str1 = "c1 may start a Java identifier is " + bool1;
        String str2 = "c2 may start a Java identifier is " + bool2;

        // Print bool1, bool2 values
        System.out.println(str1);
        System.out.println(str2);
    }
}

Output:

c1 may start a Java identifier is false
c2 may start a Java identifier is true

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

Character.isJavaIdentifierStart() Method in Java

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