使用 String 时，构造函数不能应用于给定类型

Question

Can anyone tell me where i have gone wrong in creating a construtor to call a method in another class file. It tells me constructor cannot be applied to given type

Answer 1

If you remove your constructor declaration from the Student class, then the implicit empty constructor will exist. But if you declared explicitly a constructor like your public Student(String firstname, String surname, String total) then the empty constructor won't be available, unless you add it explicitly to your class.

public Student() { };

Then you call unexistant methods :

newStudent.firstName("my name");

The method you want to call, as declared in your Student object is setFirstName(String firstName)

Finally in your println calls, you are trying to access the attribut of the object directly instead of using the getters methods.

Answer 2

You Student class don't have an empty constructor like youd do :

Student newStudent = new Student();

So you have a Constructor which should take three String :

public Student(String firstname, String surname, String total) {

So to solve your problem you have two ways :

1st

Create an empty constructor that not take any attribute like this :

public Student() {
}

and you can put your values with setAtt for example :

newStudent.setFirstName("my name");

2ed

You should to call your constructor with the three value like this :

Student newStudent = new Student("name 1", "name 2", "name 3");

Note

You can't set a value to an attribute in another class like this :

newStudent.firstName("my name");

You can make it like this :

newStudent.firstName = "my name";

Answer 3

Some change I made to correct the code :

public class Main {
    public static void main(String[] args) {
        Student newStudent = new Student("Toto", "FromStack");
        newStudent.setFirstName("Jack");
        System.out.println(newStudent.getFirstName());
        System.out.println(newStudent.getSurname());
        System.out.println(newStudent.getFullName());
    }
}

• You have to call the constructor with the good number of parameters

• Prefer set the visibility of the parameter as private (look in Student ) and use Getters to acces to them

• Also use Setters to changes the values

And here too :

public class Student {
    private String firstName;
    private String surname;

    public Student(String firstname, String surname) {
        this.firstName = firstname;
        this.surname = surname;
    }
    // First Name GETTER
    public String getFirstName() {
        return firstName;
    }
    // First Name SETTER
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    // Surname GETTER
    public String getSurname() {
        return surname;
    }
    // Surname SETTER
    public void setSurname(String surname) {
        this.surname = surname;
    }
    //Full Name GETTER
    public String getFullName() {
        return firstName+" "+surname;
    }
}

• If you're using Eclipse IDE it cans creat for you the Getters and Setters for you (in Source )

• You don't need a total attribut because it's just a concatenation of the 2 others, you will never change it alone, if it changes it will be because of a change in one of the 2 attributs, so just a getFulName() which will get back both names

And for end you can create an empty constructor if you want to sets the value after, ="" is not get "null" value for each

 public Student() {
            this.firstName = "";
            this.surname = "";
    }