How do I know if a character is lowercase?

By Wayan in Core API, Lang Package 0 Comment

In this example you are going to learn another example on using the java.lang.Character class. The Character.isLowerCase() method can be used to determine if a letter is a lowercase letter. This method takes a char as argument and return a boolean value. If it returns true it means the character is in lowercase form. And if it returns false it means the character is not in lowercase form.

Beside using the isLowerCase() method you can also compare the character type with the constant value of Character.LOWERCASE_LETTER. To get the character type you can use the Character.getType() method. You can see the example on the following code snippet.

package org.kodejava.lang;

public class CharacterIsLowerCaseExample {
    public static void main(String[] args) {
        char a = 'a';

        // Checks to see if a letter is a lowercase letter.
        if (Character.isLowerCase(a)) {
            System.out.println(a + " is a lowercase letter.");
        }

        // Checks to see if a letter is a lowercase letter
        // by comparing the character type against
        // Character.LOWERCASE_LETTER constant value.
        int charType = Character.getType(a);
        if (charType == Character.LOWERCASE_LETTER) {
            System.out.println(a + " is a lowercase letter.");
        }
    }
}

This example give you the following output:

a is a lowercase letter.
a is a lowercase letter.

How do I check if a character representing an alphabet?

By Wayan in Core API, Lang Package 2 Comments

In the previous example you’ve learned how to use the Character.isDigit() method to check if a character representing a digit.

In this example you will learn how to check if a character representing a letter. You can use the Character.isLetter(char c) method to check if a character is a valid letter. This method will return a true value for a valid letter characters and false if the character is not a valid letter.

In the code snippet below you will also learn how to use the toCharArray() method to covert a string into an array of char. Here we use the method so that we can check every character in the for-each loop to see is the character is a letter or not.

package org.kodejava.lang;

public class CharacterIsLetterExample {
    public static void main(String[] args) {
        String name = "Kode Java 123";

        // Determines if the specified character is a letter
        if (Character.isLetter(name.charAt(5))) {
            System.out.println("The fifth character (" +
                    name.charAt(5) + ") is an alphabet!");
        }

        // Iterates all characters in the string to see if it is
        // a letter or not.
        for (char c : name.toCharArray()) {
            if (Character.isLetter(c)) {
                System.out.println(c + " is a letter.");
            } else {
                System.out.println(c + " not a letter.");
            }
        }
    }
}

The code will print the following output:

The fifth character (J) is an alphabet!
K is a letter.
o is a letter.
d is a letter.
e is a letter.
  not a letter.
J is a letter.
a is a letter.
v is a letter.
a is a letter.
  not a letter.
1 not a letter.
2 not a letter.
3 not a letter.

How do I check if a character representing a number?

By Wayan in Core API, Lang Package 0 Comment

For validation purposes we might need to check if data entered by our users is a valid data for our application to process. A simple mechanism for checking if a character inputted is a digit or not can be done by using the java.lang.Character class isDigit(char c) method.

In this example you will learn how to check if a character representing a number. You will start by creating a string that contains some random alphanumeric characters in it. And then you are going to iterate these characters, get the value at the specific location using the charAt() method. In the last section you are going to check to if the character represent a digit or not.

package org.kodejava.lang;

public class CharacterIsDigitExample {
    public static void main(String[] args) {
        // Manually creates a string with randoms characters.
        String str = "12?XYZ4!6cba78+HI@0";

        for (int i = 0; i < str.length(); i++) {
            // Determines if the specified character is a digit
            if (Character.isDigit(str.charAt(i))) {
                System.out.println(str.charAt(i) + " is a digit.");
            } else {
                System.out.println(str.charAt(i) + " not a digit.");
            }
        }
    }
}

These are the outputs of our program:

1 is a digit.
2 is a digit.
? not a digit.
X not a digit.
Y not a digit.
Z not a digit.
4 is a digit.
! not a digit.
6 is a digit.
c not a digit.
b not a digit.
a not a digit.
7 is a digit.
8 is a digit.
+ not a digit.
H not a digit.
I not a digit.
@ not a digit.
0 is a digit.

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