1.4-2_Creating and Compiling Packages

Question 1

If no package defined, where is the code placed?

Answer 1

When NO package statement present, the code is placed in what is known as the “default package”.

Question 2

Which strategy should we use to avoid naming conflicts and reuse of your code?

Answer 2

Always name your packages

Question 3

How to compile ClassA and ClassB via terminal?
├── packagea
   │ ├── ClassA.class
   │ └── ClassA.java
   └── packageb
       ├── ClassB.class
       └── ClassB.java

Answer 3

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

🤯️Notice that when defining a package we use dot notation.
⚠️When compiling we use / (forward slash) referencing the directory structure.

Question 4

How to compile packages using wildcards?

Answer 4

$ javac packagea/.java packageb/.java

Question 5

What is the difference between path & classpath?

Answer 5

PATH is the environment variable where we specify the locations of binaries.
CLASSPATH is the path for Java application where the classes you compiled will be available.

Question 6

How to use an alternate target directory when compiling?

Answer 6

$ javac -d classes packagea/MyClass.java
When compiling the -d option specifies the target directory for placing the .class files, otherwise it will be placed in the same path of the class being compiled.
⚠️ Java options are case sensitive. This means you cannot pass -D instead of -d.

Question 7

What does indicate the period (.) when included as a directory in the classpath?

Answer 7

The period (.) indicates you want to include the current directory in the classpath.

Question 8

How to compile with JAR files?

Answer 8

$jar -cvf myNewFile.jar .
$jar –create –verbose –file myNewFile.jar .
(-c | –create) Create
(-v | –versose) Print details
(-f | –filename) JAR filename
(-C) Target directory to create the JAR from

Question 9

How to specify a Target Directory when creating a JAR?

Answer 9

(-C) Target directory to create the JAR from

jar -cvf myNewFile.jar -C dir .