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The java.lang.Character.digit() is an inbuilt method in java which returns the numeric value of the character ch in the specified radix. It returns -1 if the radix is not in the range MIN_RADIX <= radix <= MAX_RADIX or if the value of ch is not a valid digit in the specified radix. A character is a valid digit if at least one of the following is true:

The method isDigit is true of the character and the Unicode decimal digit value of the character (or its single-character decomposition) is less than the specified radix. In this case the decimal digit value is returned.
The character is one of the uppercase Latin letters ‘A’ through ‘Z’ and its code is less than radix + ‘A’ – 10. In this case, ch – ‘A’ + 10 is returned.
The character is one of the lowercase Latin letters ‘a’ through ‘z’ and its code is less than radix + ‘a’ – 10. In this case, ch – ‘a’ + 10 is returned.
The character is one of the fullwidth uppercase Latin letters A (‘\uFF21’) through Z (‘\uFF3A’) and its code is less than radix + ‘\uFF21’ – 10. In this case, ch – ‘\uFF21’ + 10 is returned.
The character is one of the fullwidth lowercase Latin letters a (‘\uFF41’) through z (‘\uFF5A’) and its code is less than radix + ‘\uFF41’ – 10. In this case, ch – ‘\uFF41’ + 10 is returned.

Syntax:

public static int digit(char ch, int radix)

Parameters:The function accepts two parameters which are described below:

ch- This is a mandatory parameter which specifies the character to be converted.
radix- This is a mandatory parameter which specifies radix.

Return value: This method returns the numeric value represented by the character in the specified radix. Below programs demonstrates the above method: Program 1:

Java

// Java program to illustrate the
// Character.digit() method

import java.lang.*;

public class gfg {

    public static void main(String[] args)
    {
        // create and assign value
        // to 2 character objects
        char c1 = '3', c2 = '6';

        // assign the numeric value of c1 to in1 using radix
        int in1 = Character.digit(c1, 5);
        System.out.println("Numeric value of " + c1 + " in radix 5 is " + in1);

        // assign the numeric value of c2 to in2 using radix
        int in2 = Character.digit(c2, 15);
        System.out.println("Numeric value of " + c2 + " in radix 15 is " + in2);
    }
}

Output:

Numeric value of 3 in radix 5 is 3
Numeric value of 6 in radix 15 is 6

Program 2:

Java

// Java program to illustrate the
// Character.digit() method
// when -1 is returned
import java.lang.*;

public class gfg {

    public static void main(String[] args)
    {

        // create and assign value
        // to 2 character objects
        char c1 = 'a', c2 = 'z';

        // assign the numeric value of c1 to in1 using radix
        int in1 = Character.digit(c1, 5);
        System.out.println("Numeric value of " + c1 + " in radix 5 is " + in1);

        // assign the numeric value of c2 to in2 using radix
        int in2 = Character.digit(c2, 15);
        System.out.println("Numeric value of " + c2 + " in radix 15 is " + in2);
    }
}

Output:

Numeric value of a in radix 5 is -1
Numeric value of z in radix 15 is -1

Reference: https://docs.oracle.com/javase/7/docs/api/java/lang/Character.html#digit(char,%20int)

Character.digit() in Java with examples

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