Java

Question 1

What are accessor methods?

Answer 1

Methods used to obtain information about an object.

Ex) the .length() method which returns the number of characters contained in the string object.

Question 2

Describe a nested if statement

Answer 2

A nested if statement allows you to use an if statement inside another if statement.

Question 3

Describe usage of “this” : to refer to current class instance variable

Answer 3

If there is ambiguity between the instance variables and parameters, “this” keyword resolves the problem of ambiguity.

Question 4

Describe an if statement

Answer 4

An if statement consists of a Boolean expression followed by one or more statements.

Question 5

What are the 3 types of loops in Java?

Answer 5

1. While loop
2. For loop
3. Do…while loop

Question 6

Describe Java

Answer 6

A general purpose computer-programming language that is class-based and object-oriented. It’s designed to write once and run anywhere, meaning that compiled Java code can run on all platforms without the need for recompilation.

Question 7

What is an interface?

Answer 7

An interface is a reference type in Java. It’s similar to a class. It’s a collection of abstract methods. It contains behaviors that a class implements.

Question 8

Describe a switch statement

Answer 8

A switch statement allows a variable to be tested for equality against a list of values.

Each values is a case, and the variable being switched on is checked for each case.

Question 9

What are exceptions?

Answer 9

Exceptions are events that occur during the execution of programs that disrupt the normal flow of instructions

An object that wraps around an error event that occurred within a method. Can be checked, unchecked, or errors

Question 10

What is an Array?

Answer 10

An array is a collection of similar types of elements that have a contiguous memory location. We can only store a fixed set of elements in a Java array.

Question 11

Describe the “new” keyword

Answer 11

The “new” operator instantiates a class by dynamically allocating memory for a new object and returning a reference to that memory. This reference is then stored in a variable.

The new operator is also followed by a call to a class constructor, which initializes the new object. A constructor defines what occurs when an object of a class is created.

When you declare a class in Java, you are just creating a new data type. A class provides the blueprint for objects. You can create an object from a class.

Question 12

Describe “this” : to invoke current class constructor

Answer 12

The this() constructor call can be used to invoke the current class constructor. It’s used to reuse the constructor (constructor chaining).

Question 13

Describe using “super” to invoke parent class method

Answer 13

The super keyword can also be used to invoke parent class method. It should be used if subclass contains the same method as the parent class. in other words, it is used if method is overridden.

Question 14

What are unchecked exceptions?

Answer 14

Errors, and runtime exceptions are unchecked. The compiler does not enforce (check) that you handle them explicitly.

Question 15

What are decision making structures?

Answer 15

They have one or more conditions to be evaluated or tested by the program, along with statements to be executed if the condition is true, and optionally other statements to be executed if the statement is false.

Question 16

Describe using “super” to invoke parent class constructor

Answer 16

The super keyword can also be used to invoke the parent class constructor

Question 17

Describe a for loop

Answer 17

A for loop is a repetition control structure that allows you to efficiently write a loop that needs to be executed a specific number of times.

It’s useful when you know how many times a task is to be repeated.

INITIALIZATION - allows you to declare and initialize any loop control variables.
BOOLEAN - evaluated to determine control.
BODY - after the body is executed after a true statement, control jumps back to the update statement and the boolean expression is evaluated again.

Question 18

Describe “this” : to invoke current class method

Answer 18

You may invoke the method of the current class by using the “this” keyword. If this isn’t used, the compiler will automatically add this keyword while invoking the method.

Question 19

Describe using “super” to refer to parent class instance variable

Answer 19

We can use super keyword to access the data member or field of parent class. It is used if parent class and child class have same fields.

Question 20

Describe the static keyword

Answer 20

The static keyword is used for memory management. The static keyword belongs to the class than an instance of the class. It can be: variable, method, block, nested class

Question 21

What does it mean to concatenate string?

Answer 21

To join multiple strings together.

Ex) the concat() method works with string literals.

Question 22

What are checked exceptions?

Answer 22

They are the ones that the compiler enforces that you handle them explicitly. Methods that generate checked exceptions must declare that they throw them.

Question 23

Describe static variable

Answer 23

The static variable can be used to refer to the common property of all objects. It makes your program memory efficient.

For ex. The company name of employees, college name of students

Question 24

Describe loops in Java

Answer 24

Loop statements allow us to execute a block of code several number of times.

Question 25

Describe the usage of the “super” keyword

Answer 25

The super keyword in Java is a reference variable which is used to refer immediate parent class object

Question 26

Describe an if…else if statement

Answer 26

An if statement that is followed by an else…if statement, which is useful to test various conditions using a single if…else if statement

Question 27

What is a java package?

Answer 27

A java package is a group of similar types of classes, interfaces ,and sub-packages. They are used to categorize the classes and interfaces so that they can be easily maintained.

Can be built-in or user-defined. Ex) lang, util, sql

Question 28

Describe the “this” keyword

Answer 28

“this” is a reference variable that refers to the current object.

Question 29

What is an ArrayList

Answer 29

An arraylist is part of collection framework and is in the java.util package. Can be useful in programs where lots of manipulation in the array is needed.

Question 30

Describe a do…while loop

Answer 30

A do…while loop is similar to a while loop, except that a do..while loop is guaranteed to execute at least once.

Question 31

Describe the final keyword.

Answer 31

The final keyword in java is used to restrict the user. It can be used on a: variable, method, class

Question 32

What is a String in Java?

Answer 32

Strings are a sequence of characters. They are treated as objects. The Java platform provides the String class to create and manipulate strings.

The String class is immutable, so once it is created, it cannot be changed.

Question 33

Name the 4 types of decision making statements

Answer 33

1. if statement
2. if…else statement
3. nested if statement
4. switch statement

Question 34

Describe a while loop

Answer 34

A while loop statement repeatedly executes a target statement as long as a given condition is true. When the condition becomes false, program control passes to the line immediately following the loop.

Question 35

Describe an if…else statement

Answer 35

An if…else statement is an if statement followed by an else statement to be executed when the Boolean expression is false.