Java は大文字から小文字への変換を実装します

String str = "AbC";

System.out.println(str.toLowerCase());

import java.util.Scanner; public class Exercies3 { public static void main(String[] args) { Scanner scan = new Scanner(System.in); System.out.print("输入大写字母:"); char ch = scan.next().charAt(0); while (ch <'A'|| ch > 'Z') { System.out.print("输入错误,请重新输入："); ch =scan.next().charAt(0); } ch = (char) (ch + 32);//根据ASCII码，大写字母变为小写字母只需要+32即可 System.out.print("小写字母:" + ch); } }