Java错误:无法将void转换为字符串
我知道有类似的帖子,但我似乎无法解决我的问题。我觉得它很小,但我的方法确实返回了一个字符串,所以我不知道为什么它告诉我键入void。我是java新手,希望能得到任何帮助。这是我的密码:Java错误:无法将void转换为字符串,java,compiler-errors,incompatibletypeerror,Java,Compiler Errors,Incompatibletypeerror,我知道有类似的帖子,但我似乎无法解决我的问题。我觉得它很小,但我的方法确实返回了一个字符串,所以我不知道为什么它告诉我键入void。我是java新手,希望能得到任何帮助。这是我的密码: import java.io.File; import java.io.FileNotFoundException; import java.util.Scanner; import java.security.MessageDigest; public class Login{ public stat
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.security.MessageDigest;
public class Login{
public static void main(String []args){
Scanner user_input = new Scanner(System.in);
String entered_username = Get_Credentials.get_username(user_input);
String entered_password = Get_Credentials.get_password(user_input);
String encrypted_password = MD5Digest.encrypt(entered_password);
user_input.close();
User[] all_users = File_Scanner.create_users();
}
}
class Get_Credentials{
public static String get_username(Scanner user_input){
System.out.println("Username: ");
return user_input.next();
}
public static String get_password(Scanner user_input){
System.out.println("Password: ");
return user_input.next();
}
}
class File_Scanner{
public static User[] create_users(){
User users[] = new User[6];
int index_counter = 0;
try {
File credentials_file = new File("credentials.txt");
String pattern = "[^\"\\s]+|\"(\\\\.|[^\\\\\"])*\"";
Scanner file_reader = new Scanner(credentials_file);
while (file_reader.hasNextLine()) {
users[index_counter] = new User();
users[index_counter].username = file_reader.findInLine(pattern);
users[index_counter].encrypted_password = file_reader.findInLine(pattern);
users[index_counter].password = file_reader.findInLine(pattern);
users[index_counter].role = file_reader.findInLine(pattern);
file_reader.nextLine();
index_counter++;
}
file_reader.close();
}
catch (Exception e) {
System.out.println(e.getClass());
}
return users;
}
}
class User {
String username;
String password;
String encrypted_password;
String role;
}
class MD5Digest {
public static void encrypt(String original) throws Exception {
MessageDigest md = MessageDigest.getInstance("MD5");
md.update(original.getBytes());
byte[] digest = md.digest();
StringBuffer sb = new StringBuffer();
for (byte b : digest) {
sb.append(String.format("%02x", b & 0xff));
}
System.out.println("original:" + original);
System.out.println("digested:" + sb.toString());
}
}
以下是我得到的错误:
Login.java:15: error: incompatible types: void cannot be converted to String
encrypted_password = MD5Digest.encrypt(entered_password);
^
1 error
函数没有返回值void,您尝试将其分配给字符串变量,这就是错误消息的含义 因此,改变:
public static void encrypt(String original) throws Exception {
到
及
所以这个类看起来像:
class MD5Digest {
public static String encrypt(String original) throws Exception {
MessageDigest md = MessageDigest.getInstance("MD5");
md.update(original.getBytes());
byte[] digest = md.digest();
StringBuffer sb = new StringBuffer();
for (byte b : digest) {
sb.append(String.format("%02x", b & 0xff));
}
System.out.println("original:" + original);
System.out.println("digested:" + sb.toString());
return sb.toString();
}
}
顺便说一句:注意Java的命名约定。类名应该是主题
编辑:
由于加密消息引发异常,因此您还必须在public static void mainString[]args throws exception{中引发异常,或者必须在try-catch块中处理异常。在代码中,您没有为MD5Digest类中的方法encrypt返回任何内容,如下所示:
public static void encrypt(String original) throws Exception
class MD5Digest {
public static String encrypt(String original) throws Exception {
MessageDigest md = MessageDigest.getInstance("MD5");
md.update(original.getBytes());
byte[] digest = md.digest();
StringBuffer sb = new StringBuffer();
for (byte b : digest) {
sb.append(String.format("%02x", b & 0xff));
}
System.out.println("original:" + original);
System.out.println("digested:" + sb.toString());
return sb.toString();
}
}
这就是为什么编译器会给出错误,因为它是void类型,但代码是字符串
看起来您想要返回一个字符串,它应该如下所示:
public static void encrypt(String original) throws Exception
class MD5Digest {
public static String encrypt(String original) throws Exception {
MessageDigest md = MessageDigest.getInstance("MD5");
md.update(original.getBytes());
byte[] digest = md.digest();
StringBuffer sb = new StringBuffer();
for (byte b : digest) {
sb.append(String.format("%02x", b & 0xff));
}
System.out.println("original:" + original);
System.out.println("digested:" + sb.toString());
return sb.toString();
}
}
看看您的MD5Digest类和encrypt方法。它是否返回字符串?该类位于底部。不,它只是打印原始密码和加密密码。不返回任何值。哇。我不敢相信我忘记了返回语句。谢谢!谢谢!我已更改代码以匹配您的,但现在我收到一个新错误:Login.java:12:错误:未报告的异常;必须被捕获或声明为抛出|字符串加密_password=MD5Digest.encryptentered _password;非常感谢!您是一个救生员!