Head First Java Chapter 01 — Breaking the Surface

Hello Readers,

This article is to highlight the main points include in the chapter.

• Write-once / Run anywhere, Because Java is consider as a Platform Independent Language.

The way Java works

• Write the Source code → Compile the Source Code → Compiler Creates the Java Bytecode (.class) → Bytecode can run on any device through JVM

Source: Head First Java

Structure of a class

• When the JVM starts running, JVM looking for a especial class called main

• Then JVM executing every lines in main class inside the {}.

Source: Head First Java

What can you say in the main method?

• Your code can tell JVM to:

1. Do Something — Statements : declaration, assignments, method calls, etc.
2. Do Something Again and Again — Loops : For, While, Do While loops
3. Do Something Under a Condition — Branches : If Else, Switch cases

Loops

The key to a loop is the conditional test. In Java, a conditional test is an expression that results in a Boolean value — in other words, something that is either true or false.

You can do a simple Boolean test by checking the value of a variable, using a comparison operator including:

• < (Less than)
• > (Greater Than)
• == (Equality)

Condition Branches

In Java, an if test is basically the same as the Boolean test in a while loop — except instead of saying, “while there’s still beer…”, you’ll say, “if there’s still beer…” (Source: Head First Java)

BULLET POINTS

• Statements end in a semicolon ;
• Code blocks are defined by a pair of curly braces { }
• Declare an int variable with a name and a type: int x;
• The assignment operator is one equals sign =
• The equals operator uses two equals signs ==
• A while loop runs everything within its block (defined by curly braces) as long as the conditional test is true.
• If the conditional test is false, the while loop code block won’t run, and execution will move down to the code immediately after the loop block.
• Put a Boolean test inside parentheses: while (x == 4) { }