Java Basics (Data Types, Variables, Literals)

🔹 Data Types

  • Definition: Parang “category” ng data na sinasave sa memory.
    Example: Name → characters, Age → numbers, Address → alphanumeric.

  • Dalawang klase:

    1. Primitive (standard) → built-in sa Java (basic na types).

    2. Abstract (derived) → based on primitives pero mas may features (e.g., String).

🔹 Primitive Data Types (8 total)

Ito yung pinaka-basic, hindi sila objects, wala silang methods.

  1. byte – maliit na integer, range -128 to 127, size 8-bit.
    👉 Useful kung tipid sa memory.

  2. short – mas malaki kaysa byte, range -32,768 to 32,767, size 16-bit.

  3. int – pinaka-common integer, range -2.1B to +2.1B, size 32-bit.
    👉 Default choice kapag may integer computations.

  4. long – super laki ng kaya niyang i-hold, suffix L, size 64-bit.

  5. float – single precision decimal, suffix f, size 32-bit.
    👉 Pwede sa pera (dollars/cents).

  6. double – double precision decimal, mas accurate, size 64-bit.
    👉 Default choice kapag may decimal computations.

  7. char – single character (Unicode), size 16-bit.
    👉 Pwedeng letters, numbers, symbols.

  8. boolean – logical values lang: true/false.

🔹 Integer Types

  • Java integers are always signed (may positive & negative).

  • Special note: May “unsigned right shift” operation si Java para ma-handle high-order bit (sign bit).

🔹 Floating Point Types

  • Float → single precision, mas mabilis pero less accurate.

  • Double → double precision, mas accurate, mas malaki ang kaya.

🔹 Character Types

  • ASCII (Byte) → basic letters/numbers.

  • Unicode (Char) → pang-international characters (Latin, Asian, etc.).

🔹 Boolean

  • True/false lang.

  • Output ng relational operators (>, <, ==).

🔹 Abstract Data Types

  • Based sa primitive pero upgraded.

  • Example: String → kayang mag-store ng letters, digits, symbols, words.
    ✨ Pero: di pwede gamitin for mathematical calculations kahit numbers yung laman.

🔹 Constants vs Variables

  • Variable → value can change (e.g., age, score).

  • Constant → fixed, hindi na pwede i-update once assigned.

🔹 Variable Naming Rules & Conventions

  • Dapat meaningful (para hindi ka malito).

  • Walang spaces or special symbols (except underscore _).

  • Dapat unique.

  • Start with letter, $, or _.

  • Keywords bawal (e.g., switch, class).

👉 Conventions:

  • Start with lowercase (e.g., studentAge).

  • If multi-word → camelCase.

  • Nouns dapat name ng variable.

🔹 Default Values (kapag hindi mo na-initialize)

  • byte → 0

  • short → 0

  • int → 0

  • long → 0L

  • float → 0.0f

  • double → 0.0d

  • char → '\u0000'

  • boolean → false

  • String/objects → null

🔹 Literals

  • Constant values na directly ginagamit.

Types:

  1. Boolean literals → true, false.

  2. Integer literals →

    • Decimal (normal numbers)

    • Octal (prefix 0)

    • Hexadecimal (prefix 0x)

    • Binary (prefix 0b)
      👉 May underscore _ pwede sa gitna for readability (pero hindi sa start or end).

  3. Floating-point literals → may decimal, kailangan ng f/F for float.

  4. Character literals → naka-single quotes 'a', pwede rin Unicode ('\u004E') or escape sequences ('\n', '\t').

  5. String literals → naka-double quotes "Hello World".

⚡ TL;DR:

  • Primitive types = basic data containers.

  • Variables = changeable, Constants = fixed.

  • Strings are special (abstract type).

  • Literals = actual values na pwede mo ilagay directly.