Question

当我在方法中放置getter和setter，然后在main方法中调用该方法时，尽管已将值设置为其他值，但我得到null值！另外，我没有从编译器收到任何错误，所以我确定这是一个逻辑错误，但我无法弄明白。

这是来自包含相关方法的类：

public class URTest {
UserRegistration _user = new UserRegistration();
public static void main(String[] args) {
   String fieldName;
   UserRegistration _user = new UserRegistration();
   URTest _run = new URTest();
   Scanner input = new Scanner(System.in);
   fieldName = input.nextLine();
   _run.test(fieldName);
   System.out.println(_user.getUsername()); 
}

public void test(String fieldName) {
    UserRegistration _user = new UserRegistration();
    Scanner input = new Scanner(System.in);
    String result;
    System.out.print("Enter " + fieldName + ": ");
    result = input.nextLine();
        while(true) {
            if(result.equals("")) {
                System.out.print("Please enter a value for the " + fieldName + ": ");
                result = input.nextLine();
            } else {
                break;
            }
            if(fieldName.equals("username")) {
                _user.setUsername(result);
            }
}

} }

这是包含我的getter和setter的类：

import java.io.Serializable;

public class UserRegistration implements Serializable {

private String username;
private int userId;
private String firstName;
private String lastName;
private String password;
private String email;

public UserRegistration() {
    this.username = username;
    this.userId = userId;
}

public UserRegistration(String uName, int id, String uPassword) {
    this.username = uName;
    this.userId = id;
    this.password = uPassword;
}

public String getUsername() {
    return username;
}

public void setUsername(String username) {
    this.username = username;
}

public int getUserId() {
    return userId;
}

public void setUserId(int userId) {
    this.userId = userId;
}

public String getFirstName() {
    return firstName;
}

public void setFirstName(String firstName) {
    this.firstName = firstName;
}

public String getLastName() {
    return lastName;
}

public void setLastName(String lastName) {
    this.lastName = lastName;
}

public void setPassword(String password) {
    this.password = password;
}

public String getEmail() {
    return email;
}

public void setEmail(String email) {
    this.email = email;
}

@Override
public String toString() {
    String name = getFirstName() + getLastName();
    String output = name + "has the user id " + getUserId() + 
            "username " + getUsername() + " and email " + getEmail();
    return output;
}

}

Answer 1

您正在致电

UserRegistration _user = new UserRegistration();

在你的课堂上

public UserRegistration() {
    this.username = username;
    this.userId = userId;
}

当调用上面的构造函数时，没有值设置为成员变量，因此你得到null

在你的通话方法中，

UserRegistration _user = new UserRegistration("name","id1");

OR

在构造函数中设置默认值：

public UserRegistration() {
        this.username = "name";
        this.userId = "id1";
    }

使用getter和setter获取null

1 个答案: