Introduction to object oriented programming

Which OOP principle means 'hiding internal details and showing only essential features'?

• Encapsulation

• Polymorphism

• Inheritance

• Abstraction

Answer explanation

The correct answer is 'Abstraction'. It refers to the OOP principle of hiding complex implementation details and exposing only the necessary features, allowing users to interact with objects without needing to understand their inner workings.

In Java, which of the following is not a primitive data type?

• byte

• short

• String

• boolean

Answer explanation

In Java, primitive data types include byte, short, and boolean. However, String is not a primitive type; it is an object that represents a sequence of characters. Therefore, the correct answer is String.

Which method reads an entire line of text using Scanner?

• next()

• nextChar()

• nextLine()

• readLine()

Answer explanation

The correct method to read an entire line of text using Scanner is nextLine(). The next() method reads the next token, while nextChar() and readLine() are not valid methods in the Scanner class.

The expression 17/5 in Java evaluates to:

• 3.4

• 3

• 3.0

• 4

Answer explanation

In Java, when both operands are integers, integer division is performed. Thus, 17/5 evaluates to 3, discarding the decimal part. Therefore, the correct answer is 3.

Which statement about the Math class is true?

• You must create a Math object to use its methods

• Most methods in Math are static

• Math methods require java.util import

• Math.round returns double only

Answer explanation

The correct statement is that most methods in the Math class are static, allowing them to be called without creating an instance of the class. The other options are incorrect regarding object creation, imports, and return types.

In a switch statement, the 'default' case:

• Must be the first case

• Is optional

• Must be last

• Requires a break

Answer explanation

The 'default' case in a switch statement is optional, meaning it does not have to be included. It can appear anywhere, but it is not required to be the first or last case, nor does it necessarily require a break.

System.out.print and System.out.println differ in that println:

• Prints in bold

• Flushes the buffer

• Appends a newline

• Prints to stderr

Answer explanation

System.out.println appends a newline after printing, while System.out.print does not. This means println moves the cursor to the next line, making it useful for formatting output.

Which escape sequence inserts a tab?

• \n

• \\

• \t

• \r

Answer explanation

The escape sequence \t is used to insert a tab in a string. The other options serve different purposes: \n is for a new line, \\ is a literal backslash, and \r is for a carriage return.

The condition part of a while loop is evaluated:

• After the body

• Before the body

• Only once

• Only if break is used

Answer explanation

The condition part of a while loop is evaluated before the body executes. This ensures that the loop continues only if the condition is true, making 'Before the body' the correct choice.

Which operator has the highest precedence among these?

• *

• &&

• +

• ==

Answer explanation

The '*' operator has the highest precedence among the given options. It performs multiplication and is evaluated before addition ('+') and logical operators ('&&', '=='), which have lower precedence.