Methods

Question 1

Encapsulation

Answer 1

Encapsulation is the technique used to package the information in such a way as to hide what should be hidden, and make visible what is intended to be visible. In simple terms, encapsulation generally means making the data variables private and providing public accessors.

Question 2

• Every class belongs to a package.

- A class may inherit from another class.

Answer 2

true

Question 3

• It is not required for a class to have a main method. The main method is required only if you want to execute that class directly from a command line.
• A package may have just one class as well.

Answer 3

true

Question 4

• Protected things (methods and fields) can be accessed from within the package and from subclasses.
  
  • Public things (classes, methods and fields) are accessible from anywhere.
  • No modifier means package (or default access) and is only accessible inside the package.

Answer 4

true

Question 5

Encapsulation

Answer 5

Encapsulation means that the internal representation of an object is generally hidden from view outside of the object’s definition.
Hiding the internals of the object protects its integrity by preventing users from setting the internal data of the component into an invalid or inconsistent state. A benefit of encapsulation is that it can reduce system complexity, and thus increases robustness, by allowing the developer to limit the interdependencies between software components.

Question 6

Member fields are declared private and public accessor/mutator methods are provided to access and change their values if needed.

Answer 6

true

Question 7

Overloading

Answer 7

Overloading of a method occurs when the name of more than one methods is exactly same but the parameter lists are different.
If there is another method with the same name but with a different number of arguments in a class then that method can be called as overloaded.

Question 8

Private Access

Answer 8

Only code in the same class can call private methods or access private fields.

Question 9

Default (Package Private) Access

Answer 9

When there is no access modifer, Java uses the default, which is package private access. This means that the member is “private” to classes in the same package. In other words, only classes in the package may access it.

Question 10

Protected Access

Answer 10

Protected access allows everything that default (package private) access allows and more.
The protected access modifer adds the ability to access members of a parent class.

Question 11

Public Access

Answer 11

Public means anyone can access the member from anywhere.

Question 12

static methods have two main purposes

Answer 12

■ For utility or helper methods that don’t require any object state. Since there is no need to access instance variables, having static methods eliminates the need for the caller to instantiate the object just to call the method.
■ For state that is shared by all instances of a class, like a counter. All instances must share the same state. Methods that merely use that state should be static as well.

Question 13

Regular imports vs. Static imports

Answer 13

Regular imports are for importing classes.

Static imports are for importing static members of
classes. Just like regular imports, you can use a wildcard or import a specifc member.

Question 14

Java uses pass-by-value to get data into a method.

Assigning a new primitive or reference to a parameter doesn’t change the caller. Calling methods on a reference to an object does affect the caller.

Answer 14

true

Question 15

overloading

Answer 15

Everything other than the method signature can vary for overloaded methods. This means there can be different access modifers, specifers (like static), return types, and exception lists.

Question 16

Constructor

Answer 16

Constructor is a special method that matches the name of the class and has no return type.

public class Bunny {
public Bunny() {
System.out.println("constructor");
     }
}

Question 17

Order of Initialization

Answer 17

1. If there is a superclass, initialize it first.
2. Static variable declarations and static initializers in the order they appear in the file.
3. Instance variable declarations and instance initializers in the order they appear in the file.
4. The constructor.

Question 18

Private constructor

Answer 18

Having a private constructor in a class tells the compiler not to provide a default noargument constructor. It also prevents other classes from instantiating the class. This is useful when a class only has static methods or the class wants to control all calls to create new instances of itself.

Question 19

this()

Answer 19

When this is used as if it were a method, Java calls another constructor on the same
instance of the class.

If you choose to call it, the this() call
must be the frst noncommented statement in the constructor.

Question 20

JavaBeans

Answer 20

JavaBeans are reusable software components. JavaBeans call an instance variable a property.

Question 21

A constructor cannot be final, static or abstract.

Answer 21

+

A constructor cannot return anything. Not even void.

Question 22

Multiple type inheritance

Answer 22

Java allows a class to implement multiple interfaces. An interface is a “type” and does not contain any state. This implies that Java supports multiple type inheritance.

Question 23

Multiple state inheritance

Answer 23

A class contains state and extending a class means inheriting the state. Since Java does not allow a class to extend from multiple classes, it means that Java does not support multiple state inheritance.

Question 24

Java supports Pass by Value for everything

Answer 24

. Primitives are always passed by value.
. Object “references” are passed by value. So it looks like the object is passed by reference but actually it is the value of the reference that is passed.

Question 25

“pass-by-value”

Answer 25

Java is a “pass-by-value” language. This means that a copy of the variable is made and the method receives that copy.

Assigning new values to those parameters in the method doesn’t affect the caller’s variables.

Question 26

Lambda

a -> a.canHop()

Answer 26

■ Specify a single parameter with the name a
■ The arrow operator to separate the parameter and body
■ A body that calls a single method and returns the result of that method

Question 27

Lambda

(Animal a) -> { return a.canHop(); }

Answer 27

■ Specify a single parameter with the name a and stating the type is Animal
■ The arrow operator to separate the parameter and body
■ A body that has one or more lines of code, including a semicolon and a return statement

Question 28

Functional interfaces

Answer 28

Interfaces that have only one method.

Question 29

Predicate

Answer 29

public interface Predicate {
boolean test(T t);
}

It’s in the package java.util.function