INTRO TO JAVA To DATA TYPES (W3Schools)

Para sa Quiz on Tuesday Source from w3school From Java Intro to Data types

What is Java?

A high-level, object-oriented programming language.

Who developed Java?

Originally by Sun Microsystems, now owned by Oracle.

What is JVM?

Java Virtual Machine — runs Java bytecode on any platform.

What is JDK?

Java Development Kit — includes compiler, JVM, and tools.

What is JRE?

Java Runtime Environment — includes JVM and libraries to run Java apps.

What is bytecode?

Intermediate code compiled from Java source, executed by JVM.

Why is Java platform-independent?

Because bytecode runs on any JVM regardless of OS.

What is an IDE?

Integrated Development Environment — e.g., IntelliJ, Eclipse.

What file extension does Java source use?

.java

What command compiles Java code?

javac MyClass.java

What is the entry point of a Java program?

public static void main(String[] args)

How do you print text in Java?

System.out.println("Hello");

What symbol ends a statement?

; (semicolon)

How are code blocks defined?

{} (open and closed curly brackets)

Is Java case-sensitive?

Yes

Can class names start with a number?

No

What keyword defines a class?

class

What keyword creates an object?

new

What is a constructor?

A method used to initialize objects.

Can a class have multiple constructors?

Yes, via constructor overloading.

Single-line comment syntax?

// comment

Multi-line comment syntax?

/* comment */

No

Do comments affect execution?

Can comments be nested?

No

Why use comments?

To explain code and improve readability.

What is a variable?

A container for storing data

How to declare an integer variable?

int x = 10;

Can variable names contain spaces?

No

What is initialization?

Assigning a value during declaration.

Can variables be reassigned?

Yes, unless declared final.

What is a constant?

A variable whose value cannot change.

How to declare a constant?

final int MAX = 100;

What is camelCase?

Naming convention where first word is lowercase, others capitalized

Naming convention where first word is lowercase, others capitalized

No

Can variable names contain special characters?

Only _ and $ are allowed.

How many primitive types are there?

8

What does byte store?

-128 to 127

What does short store?

-32,768 to 32,767

What does int store?

-2,147,483,648 to 2,147,483,647

What does long store?

-9 quintillion to 9 quintillion

What does float store?

~6–7 decimal digits

What does double store?

~15–16 decimal digits

What does Boolean store?

true or false

What does char store?

A single character

Default value of int?

0

Default value of boolean?

false

Default value of char?

'\u0000'

Default value of float?

0.0f

Default value of double?

0.0d

Default value of long?

0L

How to declare a float?

float f = 5.99f;

How to declare a double?

double d = 19.99;

How to declare a char?

char c = 'A';

How to declare a boolean?

boolean b = true;

How to declare a long?

long l = 123456789L;

What is a non-primitive type?

A type that refers to objects.

Examples of non-primitive types?

String, Array, Class

Can non-primitive types be null?

Yes

Can primitive types be null?

No

Is String a primitive type?

No

Can non-primitive types have methods?

Yes

How to declare a String?

String s = "Hello";

Can you use new with String?

Yes: String s = new String("Hello");

What is the default value of String?

null

Can you compare strings with ==? (More Advanced)

Not reliably — use .equals() instead.

What is type casting?

Converting one data type into another.

What is implicit casting?

Automatic conversion from smaller to larger type.

What is explicit casting?

Manual conversion using (type) syntax.

How to cast double to int?

int x = (int) 9.99;

What is the purpose of data types?

To define the kind of data a variable can hold

Other Types

• char

• Boolean

Floating-Point Types

• float

• double

Java Primitive Data Types

Integer Types

• byte

• short

• int

• long

Floating-Point Types

• float

• double

Other Types

• char

• Boolean

Integer Types

• byte

• short

• int

• long