Question
Which three statements are true?
1. The default constructor initialises method variables.
2. The default constructor has the same access as its class.
3. The default constructor invokes the no-arg constructor of the superclass.
4. If a class lacks a no-arg constructor, the compiler always creates a default constructor.
5. The compiler creates a default constructor only when there are no other constructors for the class.
Answer: Option B
class CoffeeCup {
private int innerCoffee;
public CoffeeCup() {
}
public void add(int amount) {
innerCoffee += amount;
}
//...
}
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(2) sounds correct as in the example below
class CoffeeCup {
private int innerCoffee;
public CoffeeCup() {
}
public void add(int amount) {
innerCoffee += amount;
}
//...
}
The compiler gives default constructors the same access level as their class.
In the example above, class CoffeeCup is public, so the default constructor is
public. If CoffeeCup had been given package access, the default constructor would
be given package access as well.
(3) is correct. The Java compiler GENERATES at least one instance initialisation
method for every class it compiles. In the Java class file, the instance initialisation
method is named "." For each constructor in the source code of a class, the Java
compiler generates one () method. If the class declares no constructors explicitly,
the compiler generates a default no-arg constructor that just invokes the superclass's
no-arg constructor. As with any other constructor, the compiler creates an () method
in the class file that corresponds to this default constructor.
(5) is correct. The compiler creates a default constructor if you do not declare any
constructors in your class.
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