Chapter 10: Development

Question 1

What does the -d option when used with the javac command?

Answer 1

-d or -destination defines the output folder for the compiled classes.

Question 2

Considering the following folders:
/home
   /sources
      /com/foo/bar/App.java
   /classes

And working dir is /home/sources

What is the command for compiling App.java and putting the result into the classes folder? And what is the result?

Answer 2

Command:
-javac -d ../classes com/foo/bar/App.java

Result:
/classes/com/foo/bar/App.class

Question 3

Given the following folders:
/home
/sources/App.java

And working dir is /home

What is the result of running the following command:
javac -d classes sources/App.java

Answer 3

Error.

Folder /classes does not exist

Question 4

Describe the command for running:

• MyApp.class
• With property myProp with value: my value
• And arguments 10 and x

Answer 4

java -DmyProp=”my value” MyApp 10 x

Question 5

How do you retrieve the system properties from java code?

Answer 5

System.getProperties();

Question 6

Describe the three ways how the args in a main method can be declared.

Answer 6

String[] args
String… args
String args[]

Question 7

What does the -cp -classpath flag do in combination with the java an javac commands?

Answer 7

-cp or -classpath defines class search locations, for example third party classes.

javac -classpath /com/apache:/com/microsoft MyApp.java

Question 8

Given the following class:

package com.foo.bar
public class MyApp {}

When compiles using:
javac -d classes MyApp.java

What is the result?

Answer 8

classes/com/foo/bar/MyApp.class

Question 9

Given the following folders:
/home
   /dirA
      /dirB
         /dirC

Working dir is Home.

What folders are searched for classes when used in:
-cp /home/dirA/dirB:dirA

Answer 9

dirB, dirA, dirC

/home/dirA/dirB is a absolute path
dirA is a relative path

Question 10

What is the /jre/lib/ext folder inside a Java installation?

Answer 10

A folder that is automatically added to the classpath by Java. Adding JAR files here will automatically add them to the classpath

Question 11

Improve the following code to use Static Imports:
public class App {
   public static void main(String[] args) {
      System.out.println(Integer.MAX_VALUE);
      System.out.println(Integer.toHexString(42);
   }
}

Answer 11

Add two static imports:
import static java.lang.System.out;
import static java.lang.Integer.*;

public class App {
   public static void main(String[] args) {
      out.println(MAX_VALUE);
      out.println(toHexString(42);
   }
}