public class HelloWorld {
??? public static void main(String[] args) {
??String fileName = "HelloWorld.java";
??String email = "[email protected]";
??????? //獲取文件名中最后一次出現"."號的位置
??int index = fileName.lastIndexOf(".");
??????? // 獲取文件的后綴
???? String prefix = (index+1,fileName.length());
??if (index != -1 && index != 0 && prefix.equals("java")) {
???System.out.println("Java文件名正確");
??} else {
???System.out.println("Java文件名無效");
??}
??????? int index2 = email.indexOf('@');
??????? // 獲取郵箱中"."號的位置
??int index3 = email.indexOf('.');
??// 判斷必須包含"@"符號，且"@"必須在"."之前
??if (index2 != -1 && index3 > index2) {
???System.out.println("郵箱格式正確");
??} else {
???System.out.println("郵箱格式無效");
??}
?}
}