Java字符串大小写转换的方法有以下几种:
String str = "hello"; String upperCaseStr = str.toUpperCase(); System.out.println(upperCaseStr); // 输出: HELLO
String str = "HELLO"; String lowerCaseStr = str.toLowerCase(); System.out.println(lowerCaseStr); // 输出: hello
String str = "hello"; char ch = str.charAt(0); char upperCaseCh = Character.toUpperCase(ch); System.out.println(upperCaseCh); // 输出: H
String str = "HELLO"; char ch = str.charAt(0); char lowerCaseCh = Character.toLowerCase(ch); System.out.println(lowerCaseCh); // 输出: h