Chapter 1: Building blocks

Question 1

The java command launches the Java Virtual Machine (JVM) before running bytecode. If false, why?

Answer 1

True

Question 2

What is type promotion in Java?

Answer 2

Type promotion automatically converts smaller or less precise types to larger or more precise types during expressions, so that operations can be performed safely without data loss.

Question 3

The javac command converts .java source files into .class bytecode. If false, why?

Answer 3

True

Question 4

The jar command is used to package multiple files together in Java. If false, why?

Answer 4

True

Question 5

The javadoc command generates documentation for Java source code. If false, why?

Answer 5

True

Question 6

A Java class can have both methods and fields. If false, why?

Answer 6

True

Question 7

The void keyword in Java means a method does not return any value. If false, why?

Answer 7

True

Question 8

Parameters in a method provide values from the calling method. If false, why?

Answer 8

True

Question 9

The javac command is used to execute Java programs. If false, why?

Answer 9

False – The javac command compiles source code into bytecode, but does not execute it.

Question 10

An object and a class in Java are the same thing. If false, why?

Answer 10

False – A class is a blueprint, while an object is an instance of that class.

Question 11

A reference variable in Java holds the actual object. If false, why?

Answer 11

False – A reference variable holds the memory address of an object, not the object itself.

Question 12

A Java class must always contain at least one method. If false, why?

Answer 12

False – A class can be empty, such as public class Animal {}.

Question 13

The simplest Java class must include a main method. If false, why?

Answer 13

False – A Java class only needs to be defined; a main method is required only for execution.

Question 14

The String class in Java is a primitive data type. If false, why?

Answer 14

False – String is a class, not a primitive type; it is an object in Java.

Question 15

The public keyword restricts a method’s access to only within the same class. If false, why?

Answer 15

False – public allows the method to be accessed from other classes.

Question 16

A single-line comment in Java starts with // and extends to the end of the line.

Answer 16

True

Question 17

A multiline comment in Java starts with /** and ends with **/.

Answer 17

(Correct: It starts with /* and ends with */.)

Question 18

Javadoc comments can only be used inside methods.

Answer 18

(Correct: Javadoc comments can be used for classes, methods, and fields.)

Question 19

Java ignores all comments, including Javadoc comments, at runtime and compile time.

Answer 19

(Correct: Javadoc comments can be processed by the Javadoc tool.)

Question 20

A Java source file can contain multiple public classes.

Answer 20

(Correct: Only one top-level class can be public.)

Question 21

If a class is not declared public, it must be declared private.

Answer 21

(Correct: A top-level class can be package-private if no access modifier is specified.)

Question 22

A Java file with a public class does not have to match the filename.

Answer 22

(Correct: The filename must match the public class name exactly.)

Question 23

The Javadoc @author tag is required for all classes.

Answer 23

(Correct: It is optional and used for documentation purposes.)

Question 24

Comments can slow down Java code execution.

Answer 24

(Correct: Comments are ignored by the compiler and do not affect execution speed.

Question 25

A Javadoc comment must include an @param tag.

Answer 25

(Correct: The @param tag is only needed if documenting method parameters.)

Question 26

What happens if a line inside a text block ends with a backslash \?

Answer 26

The backslash suppresses the automatic line break and joins the next line into one continuous line.

Question 27

Does the backslash \ at the end of a line in a text block insert a \n (newline) character?

Answer 27

No! It avoids inserting any \n. The next line is simply glued to the current one without any newlines.

Question 28

In a Java text block, what is the effect of a backslash \ at the end of a line?

Answer 28

* No new line is inserted. * It creates one continuous line in the resulting String.

Question 29

What is essential whitespace in a Java text block?

Answer 29

Essential whitespace is the part of the text block’s indentation or spaces that you intend to keep as part of the actual String content.

Question 30

Does Java automatically remove essential whitespace inside a text block?

Answer 30

No! Essential whitespace is preserved exactly in the final String — it is important and intentional.

Question 31

How does Java decide what whitespace is essential in a text block?

Answer 31

Java draws a vertical line based on the leftmost non-blank character; everything to the right of that line (including spaces) is essential and kept in the String.

Question 32

What is incidental whitespace in a Java text block?

Answer 32

Incidental whitespace is extra indentation at the beginning of lines, added just to make the code easier to read, but not intended to be part of the actual String content.

Question 33

What does Java do with incidental whitespace in a text block?

Answer 33

Java automatically removes incidental whitespace from each line when building the final String.

Question 34

How does Java identify incidental whitespace inside a text block?

Answer 34

It looks for the smallest common indentation across all non-blank lines and removes that shared indentation.

Question 35

Is variable interpolation (\\{} syntax) supported in Java 17 text blocks?

Answer 35

No. Java 17 text blocks do not support variable interpolation. You must manually concatenate values.

Question 36

In Java 17, how do you include a variable inside a text block?

Answer 36

You must concatenate manually using +, like: ``` String name = "John"; String text = """ Hello """ + name + """ Welcome! """; ```

Question 37

When did variable interpolation (\\{} syntax) officially become available in Java?

Answer 37

Variable interpolation was introduced as a preview feature in Java 21 with String Templates, not in Java 17.

Question 38

In an operation between a long and a double, which type is promoted, and what is the result type?

Answer 38

The long is promoted to double, and the result is of type double.

Question 39

List Java’s numeric promotion hierarchy (smallest to largest).

Answer 39

byte → short → int → long → float → double

Question 40

What happens when you perform arithmetic (like +, -, *, /) between two char values in Java?

Answer 40

Both char values are promoted to int before the operation. The result of the operation is an int, not a char.

Question 41

Why does Java promote char values to int during arithmetic operations?

Answer 41

Because char can only store one 16-bit character (0–65,535), but arithmetic operations might produce values larger than that. Promoting to int ensures no overflow or data loss.