Capitalize the First Letter of a String in Java

In Java, to check if a String contains only uppercase letters, we can use many approaches. These approaches verify each character in the String to ensure they are all in uppercase. A simple method, such as iterating through the characters and checking their case.

In this article, we will discuss how to check if a String contains only uppercase letters in Java.

Methods to check if a String contains only uppercase letters

Below are the three methods to check if the String contains only uppercase letters or not in Java.

• string.matches()
• Apache Commons Lang library
• Character.isUpperCase()

Program to check if a String contains only uppercase letters in Java

Below are the implementations of the above-mentioned methods to check if a String contains only uppercase letters or not.

Method 1: string.matches()

The string.matches() method in Java proves invaluable for verifying whether a given string conforms to a predefined regular expression. This functionality is particularly useful when aiming to ascertain if a string exclusively comprises uppercase letters.

Java

// Java Program to Check if String Contains Only Uppercase Letters
public class Main
{
    public static void main(String[] args)
    {
        // Sample string
        String string = "GEEKSFORGEEKS";

        System.out.println("Method 1: string.matches()");

        // to check if the string contains only uppercase letters
        if (string.matches("[A-Z]+")) {
            System.out.println("The string contains only uppercase letters.");
        } else {
            System.out.println("The string contains lowercase letters or non-alphabetic characters.");
        }
    }
}

Output

Method 1: string.matches()
The string contains only uppercase letters.

Explanation of the above Program:

• This Java program checks if a given string contains only uppercase letters.
• It uses the matches("[A-Z]+") method, which checks if the entire string consists of one or more uppercase letters.
• In simpler terms, it examines whether a word is entirely composed of capital letters or not.

Method 2: Apache Commons Lang library

It is easy method for checking the string is uppercase or not.

Java

// Java Program to Check if String Contains Only Uppercase Letters using Apache Commons Lang
import org.apache.commons.lang3.StringUtils;

public class Main
{
    public static void main(String[] args)
    {
        // Sample string
        String string = "GEEKSFORGEEKS";

        System.out.println("Method 2: Apache Commons Lang library ");

        // checks if the string contains only uppercase letters using Apache Commons Lang
        if (StringUtils.isAllUpperCase(string)) {
            System.out.println("The string contains only uppercase letters.");
        } else {
            System.out.println("The string contains lowercase letters or non-alphabetic characters.");
        }
    }
}

Output:

Method 2: Apache Commons Lang library 
The string contains only uppercase letters.

Explanation of the above Program:

• This Java program checks if a given string contains only uppercase letters using Apache Commons Lang library.
• It utilizes the StringUtils.isAllUpperCase(string) method to determine if the string consists exclusively of uppercase letters.
• In simple, it uses a specialized library to check if all the letters in a word are written in capital letters.

Method 3: Character.isUpperCase()

The core mechanism involves checking each character with the Character.isUpperCase() method in Java, which returns true if the character is an uppercase letter.

Java

// Java Program to Check if String Contains Only Uppercase Letters without External Libraries
public class Main
{
    public static void main(String[] args)
    {
        // Sample string
        String string = "GEEKFORGEEKS";
        boolean containsOnlyUppercase = true;

          System.out.println("Method 3: Character.isUpperCase() ");

        // checks if the string contains only uppercase letters
        for (char ch : string.toCharArray())
        {
            if (!Character.isUpperCase(ch))
            {
                containsOnlyUppercase = false;
                break;
            }
        }

        // Display the result
        if (containsOnlyUppercase)
        {
            System.out.println("The string contains only uppercase letters.");
        } else
        {
            System.out.println("The string contains lowercase letters or non-alphabetic characters.");
        }
    }
}

Output

Method 3: Character.isUpperCase() 
The string contains only uppercase letters.

Explanation of the above Program:

• This Java program checks if a given string contains only uppercase letters without using external libraries.
• It takes a sample string, “GEEKFORGEEKS,” and iterates through each character using a loop.
• The Character.isUpperCase(ch) method is employed to verify if each character is uppercase.
• If any lowercase letter or non-alphabetic character is found, it sets a boolean variable containsOnlyUppercase to false, breaking out of the loop.
• Finally, it prints whether the string contains only uppercase letters or not.
• In simpler terms, it manually examines each character to ensure they are all in capital letters.