String.toLowerCase() function is a very useful and common string processing function in Java, which can convert a string to lowercase form. In this article, we will introduce how to use this function and give some related code examples.

First, let us take a look at the basic syntax of the String.toLowerCase() function. It doesn't have any parameters, just call it. The following is a sample code:

String str = "Hello World";
String lowercaseStr = str.toLowerCase();
System.out.println(lowercaseStr);

The output result will be:

hello world

It can be seen that the function converts all uppercase letters in the original string into lowercase letters, and returns a new string.

In practical applications, we often need to convert the input string into lowercase for processing. For example, when users enter their username or password, we usually convert them into lowercase to avoid verification problems caused by uppercase and lowercase. The following is a code example for user login:

import java.util.Scanner;

public class LoginSystem {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        
        System.out.print("請輸入用戶名：");
        String username = scanner.nextLine();
        System.out.print("請輸入密碼：");
        String password = scanner.nextLine();
        
        // 將用戶名和密碼轉換為小寫形式
        String lowercaseUsername = username.toLowerCase();
        String lowercasePassword = password.toLowerCase();
        
        // 進行驗證
        if (lowercaseUsername.equals("admin") && lowercasePassword.equals("password")) {
            System.out.println("登錄成功！");
        } else {
            System.out.println("用戶名或密碼錯誤！");
        }
    }
}

In the above code, we first use the Scanner class to obtain the user name and password entered by the user. Then, use the String.toLowerCase() function to convert them to lowercase. Finally, we verify the username and password. In this way, regardless of whether the user enters uppercase or lowercase letters, the correct result will be obtained.

In addition to user login to the system, the String.toLowerCase() function can also be used to compare whether strings are equal. The following is a code example:

String str1 = "HELLO";
String str2 = "hello";

if (str1.toLowerCase().equals(str2.toLowerCase())) {
    System.out.println("兩個字符串相等！");
} else {
    System.out.println("兩個字符串不相等！");
}

The output result is:

The two strings are equal!

By calling the String.toLowerCase() function, we can avoid sensitivity to string case and provide more flexible and accurate string comparison.

In programming, string processing is one of the common tasks. The String.toLowerCase() function provides us with a simple and convenient way to convert strings to lowercase, making string processing more flexible and easier to operate. Whether it is user-entered strings, string comparisons, or other application scenarios, the String.toLowerCase() function can come in handy. I hope this article can help you better understand and use this important string processing function.

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