java - 使用 charAt 将字符串转换为大写

Question

我正在编写一个程序，要求用户以小写形式输入姓氏，并询问他们是否希望将其输出为全部大写或仅将第一个字母大写。我遇到的问题是将 charAt 与 toUpperCase 一起使用。

import java.util.Scanner;
//This imports the scanner class
public class ChangeCase {

    public static void main(String[] args) {
        Scanner scan = new Scanner (System.in);
        //This allows me to use the term scan to indicate when to scan
        String lastName;
        //sets the variable lastName to a string
        int Option;

    System.out.println("Please enter your last name");
    //Prints out a line
    lastName = scan.nextLine();
    //scans the next line of input and assigns it to the lastName variable
    System.out.println("Please select an option:"+'\n'+"1. Make all leters Capitalised"+'\n'+ "2. Make the First letter Capitalised");
    Option = scan.nextInt();
    if (Option == 1){
        System.out.println(lastName.toUpperCase());
    }
    if (Option == 2){
        System.out.println(lastName.charAt(0).toUpperCase());

    }
    }

}

我收到一条错误消息“无法在基本类型 char 上调用 toUpperCase()”

Answer 1

您不能像您的错误所说的那样对 char 应用 String.toUpperChase 。如果您想让第一个字母大写，您可以执行以下操作:

    String lastName = "hill";
    String newLastName = lastName.substring(0, 1).toUpperCase() + lastName.substring(1);
    System.out.println(newLastName);

运行示例:

run:
Hill
BUILD SUCCESSFUL (total time: 0 seconds)

如果您希望所有字母都大写，则很简单

    newLastName = lastName.toUpperCase();
    System.out.println(newLastName);

运行示例:

run:
HILL
BUILD SUCCESSFUL (total time: 0 seconds)