Java Notes (1) - Introduction to

The note introduces the fundamentals of the Java programming language: data types, arithmetic, and operators.

Java notes of open courses @Codecademy.

Brief Introduction

Java is a programming language designed to build secure, powerful applications that run across multiple operating systems.

The Java language is known to be flexible, scalable, and maintainable.

Data Types

• int:

  • int is short for integer, which are all positive and negative numbers, including zero.
  • The int data type only allows values between -2,147,483,648 and 2,147,483,647 (32 bits in binary representation).

• boolean:

  • A boolean is a data type that can only be either true or false. (Unlike in Python, True or False.)

• char:

  • char is short for character and can represent a single character.
  • All char values must be enclosed in single quotes, like this: 'G'.

• Variables

  • A variable stores a value.
  • In Java, all variables must have a specified data type.

Tips: A semicolon ; is also used to end all Java single code statements. We will cover statements that should not end in a semicolon later in this course. (Python codes don't need so.)

• Whitespace

  • Whitespace is one or more characters (such as a space, tab, enter, or return) that do not produce a visible mark or text. Whitespace is often used to make code visually presentable.
  • Java will ignore whitespace in code, but it is important to know how to use whitespace to structure code well.

• Comments

  • A comment is text you want Java to ignore.
  • Single line comments are one line comments that begin with two forward slashes: //.
  • Multi-line comments are generally longer comments that can span multiple lines. They begin with /* and end with */.

Arithmetic

• +: add
• -: subtract
• *: multiply
• /: divide
• %: modulo, which returns the remainder of dividing two numbers

Operators

• Relational operators

  • Relational operators compare data types that have a defined ordering, like numbers (since numbers are either smaller or larger than other numbers).
  • Relational operators will always return a boolean value of true or false.

• Equality operators

  • Equality operators are used to test equality.
  • Equality operators do not require that operands share the same ordering.

• Operators:
  - <: less than.
  - <=: less than or equal to.
  - >: greater than.
  - >=: greater than or equal to.
  - ==: equal to
  - !=: not equal to

External Resources

• Java Data Types
• Java Operators