Chapter 1

Question 1

What are the key (identifying) benefits of Java

Answer 1

• Object Oriented
• Encapsulation
• Platform independent
• Robust
• Simple
• Secure
• Multithreaded
• Backward Compatibility

Question 2

What key pieces does the Java Development Kit contain?

Answer 2

• The compiler (javac)
• The launcher (java)
• The Java Virtual Machine (JVM)
• javadoc
• jar

Question 3

What is an object?

Answer 3

A runtime instance of a class in memory

Question 4

What is a reference?

Answer 4

A variable that points to an object.

Question 5

What are the two primary elements of a Java class?

Answer 5

Methods and fields.

Question 6

What is the simplest valid Java class we can write?

Answer 6

public class Animal { }

Question 7

The method signature consists of .. ?

Answer 7

The method name and parameters.

Question 8

Does Java require a class to be public?

Answer 8

Java does not require a class to be public

Question 9

Given a file with two or more classes, how many are allowed to be public? How many must be public?

Answer 9

Only one is allowed to be public (must match file name) & none are required.

Question 10

Where does Java begin execution?

Answer 10

By calling the main() method.

Question 11

What command do we use to check the version of java?

Answer 11

java -version

Question 12

Using the terminal, how can we compile and then run the file Zoo.java?

Answer 12

1. javac Zoo.java

2. java Zoo

Question 13

Using the terminal with single-file source-code, how can we compile and then run the file Zoo.java?

Answer 13

1. java Zoo.java

Question 14

What is the constraint of single-file source-code?

Answer 14

It can only be used if your program contains one file.

Question 15

What are the differences between using the commands javac + java and single-file source-code to compile and run a program?

Answer 15

Full command

• need to use two commands
• Produces a class file
• For any program
• Can import code in any available Java library

Single-file source-code

• one command
• Fully in memory (no class files)
• For programs with one file
• Can only import code that came with the JDK

Question 16

Is using java.util.Random more efficient than using java.util.* to import the Random class?

Answer 16

Java automatically imports only the classes that are needed so in the end only Random will be importer in both cases.

Question 17

There is one special package in Java that is implicitely imported by Java. Which one is it?

Answer 17

java.lang

Question 18

What package do the Files and Paths class belong to?

Answer 18

java.nio.file

Question 19

How many wildcards (*) are allowed in a package declaration?

Answer 19

One, and it must be at the end.

Question 20

What does java do with “ties” for precedence in import declarations?

example:

import java.util.Date;
import java.sql.Date;

Answer 20

It throws an error:

- error: reference to Date is ambiquous

Question 21

Compile and run the following two classes using the java terminal commands:

• packagea/ClassA
• packageb/ClassB (contains the main method)

Answer 21

• javac packagea/ClassA.java packageb/ClassB.java

- java packageb.ClassB

Question 22

Where does the javac command place the compiled classes by default?

Answer 22

In the same directory as the source code.

Question 23

How can we use the javac command to compile ‘packagea/ClassA’ in the directory ‘classes’

Answer 23

javac -d classes packagea/ClassA.java

Question 24

Compile and run the two classes below using the java terminal commands. Compile them into a directory called ‘classes’.

• packagea/ClassA
• packageb/ClassB (contains the main method)

Answer 24

1. javac -d classes packagea/ClassA.java packageb/ClassB.java
2. java -cp classes packageb.ClassB

Question 25

What options are there to specify the classpath to the java or javac command?

Answer 25

• ‘-cp’
• ‘-classpath’
• ’–class-path’

Question 26

Create a JAR file: ‘myNewFile.jar’ based on the current directory.

Answer 26

jar -cvf myNewFile.jar .
– or –
jar –create –verbose –file myNewFile.jar .

Question 27

Create a JAR file: ‘myNewFile.jar’ based on the directory ‘dir’

Answer 27

jar -cvf myNewFile.jar -C dir .

Question 28

Is the following entry point method allowed?

• static public void main(String [ ]args) { }

Answer 28

yes