[03] Java Foundations 1Z0-811 - Basic Java Elements

This is the third installment of my Java Foundations Exam series. In this post, I delve into essential concepts like Java conventions, identifiers and reserved words, package creation and importation, the structure of a Java class, advanced compilation and execution, as well as the crucial java.lang package and other standard Java packages.

Conventions in Java

As programmers, adhering to conventions is vital for code readability. Java, being a community-driven language, follows specific conventions:

Cases

• Class Names: Start with an uppercase letter, e.g., ReadOnlyArrayList.
• Package Names: Generally lowercase, or camel case starting with a lowercase letter, e.g., datastructures or dataStructures.
• Variable Names: Start with a lowercase letter, preferably in camel case, e.g., currentAccount or current_account.

Naming

• Package Names: Follow the reverse domain convention, e.g., com.companyname.appname.

Java Identifiers and Reserved Words

Understanding identifiers and reserved words is crucial in Java programming:

• Keywords: Have special meanings and can’t be redefined. Examples include goto.
• Literals: Represent values literally, e.g., true, false, null.
• Reserved Words: Include keywords, literals, and prohibited words. var is an identifier with special meaning.

Create and Import Packages

Creating and importing packages are fundamental to organizing and reusing code:

• Package Statement: Specifies the package a class belongs to, must be the first statement or defaults to the default package.
• Import Statement: Used to make classes from other packages accessible. Avoid wildcard imports (import.*) for clarity.

Import statements are optional; you can use Fully Qualified Class Names (FQCN) directly in the code.

Structure of a Java Class

Understanding the structure of a Java class is pivotal:

• Package Statements: Zero or one, at the beginning.
• Import Statements: Zero or more, after package statements.
• Type Declarations: Zero or more (class, interface, enum).

Within a class, you can have various members such as fields, methods, constructors, and initializers.

Advanced Compilation and Execution

Compiling and executing Java programs involve understanding dependencies and package structures:

• Compilation: Compile independent classes first. For multiple classes, specify all source files or use wildcards, e.g., javac -d . *.java.
• Packaging into JAR: Use jar -cvf accounting.jar accounting to maintain package structure.

Compilation Error vs. Exception at Runtime

Differentiating compilation errors and runtime exceptions is essential:

• The compiler checks syntactical rules and logical correctness.
• JVM guards against runtime errors; anything bypassing the compiler is caught at runtime. = The java.lang and Other Standard Java Packages

Exploring the java.lang package and other standard packages is crucial:

The java.lang.Object class

• Most important class.
• Root class, ultimate parent of all classes in Java. Root of Java class hierarchy.
• If a class doesn’t extend any other class explicitly, then it implicitly extends Object.
• Object is the only class that doesn’t have a parent.
• Everything, except primitive data types, are objects in Java.
  • Primitive types represent pure data, without any behavior while reference types, contain both - data and behavior.
  • Java has object oriented versions of the primitive data types as well. The “wrapper classes”

• Java 1.5 introduced “autoboxing”, it allows seamless interoperation between primitive types and their corresponding wrapper classes.

Example:

int i= 10; //10 is a primitive value and int is a primitive type

Integer iW = 10; //assigning a primitive value 10 to a reference variable iW

iW = i; //assigning a primitive variable to reference variable

i = iW;//assigning a reference variable to a primitive variable

• If you try to assign a primitive value to its corresponding wrapper class variable, the value is automatically wrapped into the corresponding wrapper class.

The java.lang.System class

• Allows you to print output to the console.
• System.out.println
• System contains a variable named out, it is of type PrintStream, which has various print/println methods.

The java.lang.Math class

• Provides methods for computing commonly used math functions such as exponentials, trigonometric values and logarithms.
• Also has methods for rounding decimal values.

The java.lang.Random class

• Provides methods for generating random numbers.

Lais Ziegler

Dev in training... 👋

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