Records

Question 1

Can records extend other records or classes?

Answer 1

No, only implement interfaces

Question 2

Can record parameters be used in methods inside record?

Answer 2

Yes, normally

Question 3

Can record parameters auto. generated methods be overridden?

Answer 3

Yes, methods that are auto. generated from parameters can be overriden:
public record Test(int rows, int cols, String name) {
public int cols() {
return 5;
}
}

Question 4

How do we use records parameters?

Answer 4

After instantiation, we get parameters by calling parameter names as methods. eg. test.rows()

Question 5

What can records contain?

Answer 5

Other variables, methods, classes, interfaces, enums, annotations etc.

Question 6

What types of constructors does record have?

Answer 6

Long and short (compact)

Question 7

How does compact constructor look like and what is it used for?

Answer 7

public Test {}

For simple checks of the passed input parameters. This constructor cannot change input parameters.

Question 8

How does long constructor look like and what is it used for?

Answer 8

public Test(int a, int b) {

public Test(int a, int b) {
// do a check
this.a = a;
this.b = b;
}

}

Used to run checks and change input parameters.

Question 9

When are record fields set?

Answer 9

After constructor finishes

Question 10

How many compact constructors can record have?

Answer 10

Only one, and it cannot be overloaded

Question 11

How is constructor overloading done?

Answer 11

We create a new constructor with different signature that canonical (long) constructor. On its first line, we must call that canonical constructor with this(). After it is called, record is immutable.

// Canonical constructor
public Person(String name, int age) {
    if (age < 0) throw new IllegalArgumentException("Age cannot be negative");
    this.name = name;
    this.age = age;
    // Record becomes immutable here, after this constructor completes
}

// Overloaded constructor
public Person(String name) {
    this(name, 0); // Record is NOT immutable here
    // Record is immutable here, after the canonical constructor has been called and completed
}