我得到null作为结果?谁能抓住并纠正同样的谢谢

Question

我创建的方法

public class Use {
private
String firstname;
String lastname;

public String output() {
return "Hii my name is " + firstname + lastname;
}   
public String getFirstName() {
return firstname.toUpperCase();
}
public void setFirstName(String jl) {
firstname = jl.strip() ;

}
public String getLastName() {
return lastname.toUpperCase();

}
public void setLastName(String FN) {
lastname = FN.strip();
}

}

和我试图使用上面的方法在这个代码:

import java.util.ArrayList;
import java.util.List;
public class MySweetProgram {
public static void main(String[] args) {
String[] firstnames = {"KARRIK", "KESHAV", "Sussy"};
String[] lastnames = {"gulati", "gulati", "smith"};
List <User> users = new ArrayList<User>();

for (int  i = 0; i < firstnames.length;     i ++) {
User user = new User();
user.setFirstName(firstnames[i]);
user.setLastName(lastnames[i]);
users.add(user);
} 
for (User user : users) {
System.out.println(user.getfullname());
}       
}

}   

on running get null null null

Answer 1

1:在'MySweetProgram'类(Typo: User)中没有这样的'Use'类

2:在'Use, class as'getfullname()'中没有这样的方法

解决方案:将类名改为User并替换'getfullname()'与"输出()"。'

import java.util.ArrayList;
import java.util.List;
public class MySweetProgram {
public static void main(String[] args) {
String[] firstnames = { "KARRIK", "KESHAV", "Sussy" };
String[] lastnames = { "gulati", "gulati", "smith" };
List<User> users = new ArrayList<User>();
for (int i = 0; i < firstnames.length; i++) {
User user = new User();
user.setFirstName(firstnames[i]);
user.setLastName(lastnames[i]);
users.add(user);
}
for (User user : users) {
System.out.println(user.getfullname());
}
}
}
//User Class
class User {
private String firstname;
private String lastname;
public String output() {
return "Hii my name is " + firstname + lastname;
}
public String getfullname() {
return firstname + "_" + lastname;
}
public String getFirstName() {
return firstname.toUpperCase();
}
public void setFirstName(String jl) {
// firstname = jl.strip();// for java 11
firstname = jl;
}
public String getLastName() {
return lastname.toUpperCase();
}
public void setLastName(String FN) {
// lastname = FN.strip();//for java 11
lastname = FN;
}
}