Tokens, Escape Sequences, Variables & Identifiers in Java – ICSE

 📘 ICSE Notes – Java Fundamentals

✅ Tokens, Escape Sequences, Variables & Identifiers in Java

🔹 1. Escape Sequences

✅ Definition:

Escape sequences are special characters used inside output statements to perform special tasks like moving to a new line, giving space, etc.

They always start with a backslash ( \ ).

✅ Common Escape Sequences:

Escape Code	Meaning
\n	New Line
\t	Tab Space
\	Backslash
"	Double Quotes
\b	Backspace

✅ Example:

System.out.println("Hello\nWorld");

👉 Output:

Hello
World

---

🔹 2. Tokens

✅ Definition:

Tokens are the smallest units of a Java program.

✅ Types of Tokens:

1. Keywords

2. Identifiers

3. Literals

4. Operators

5. Separators

---

🔹 3. Reserved Keywords

✅ Definition:

Keywords are special reserved words in Java that have predefined meanings.

👉 They cannot be used as variable names.

✅ Examples:

int, class, public, static, void, if, else, while, return

---

🔹 4. Identifiers

✅ Definition:

Identifiers are the names given to variables, classes, methods, etc.

✅ Example:

int marks;
String name;

Here:

• marks → identifier

• name → identifier

---

🔹 5. Naming Rules for Identifiers

✅ Rules:

1️⃣ Must start with:

• letter OR underscore (_)

2️⃣ Cannot start with number

❌ 2marks (Wrong)
✅ marks2 (Correct)

3️⃣ No spaces allowed

❌ total marks
✅ totalMarks

4️⃣ Cannot be a keyword

❌ int class
✅ int className

5️⃣ Special symbols not allowed except _ and $

---

🔹 6. Literals (Constants)

✅ Definition:

Literals are fixed values that do not change during program execution.

✅ Types:

Type	Example
Integer Literal	10, 25
Float Literal	3.14
Character Literal	'A'
String Literal	"Hello"
Boolean Literal	true, false

---

🔹 7. Variables

✅ Definition:

A variable is a named memory location used to store data.

👉 Value of variable can change during program execution.

✅ Example:

int age = 15;

Here:

• age → variable

• 15 → value

---

🔹 8. Variable Declaration & Initialization

✅ Declaration:

Creating a variable.

Example:

int marks;

---

✅ Initialization:

Assigning value to variable.

Example:

marks = 90;

---

✅ Declaration + Initialization Together:

int marks = 90;

---

📊 QUICK REVISION TABLE

Topic	Simple Meaning
Escape Sequence	Special characters for formatting output
Tokens	Smallest units of program
Keywords	Reserved words
Identifiers	Names given to variables
Literals	Fixed values
Variables	Store data
Declaration	Creating variable
Initialization	Assigning value

---

🧠 MIND MAPS 

---

🧠 1. Escape Sequence Mind Map

Escape Sequences
   │
   ├── \n → New Line
   ├── \t → Tab
   ├── \" → Quotes
   ├── \\ → Backslash
   └── Used in Output Formatting

---

🧠 2. Tokens Mind Map

Tokens
 │
 ├── Keywords
 ├── Identifiers
 ├── Literals
 ├── Operators
 └── Separators

---

🧠 3. Keywords Mind Map

Keywords
 │
 ├── Reserved Words
 ├── Predefined Meaning
 ├── Cannot be used as names
 └── Examples: int, class, if

---

🧠 4. Identifiers Mind Map

Identifiers
 │
 ├── Names of variables
 ├── Names of classes
 ├── Names of methods
 └── Follow naming rules

---

🧠 5. Naming Rules Mind Map

Identifier Rules
 │
 ├── Start with letter or _
 ├── No spaces
 ├── No keywords
 ├── No special symbols
 └── Cannot start with number

---

🧠 6. Literals Mind Map

Literals
 │
 ├── Integer
 ├── Float
 ├── Character
 ├── String
 └── Boolean

---

🧠 7. Variables Mind Map

Variables
 │
 ├── Store Data
 ├── Value can change
 ├── Has Name
 └── Has Data Type

---

🧠 8. Declaration & Initialization Mind Map

Variables
 │
 ├── Declaration → int x;
 ├── Initialization → x = 10;
 └── Both Together → int x = 10;





Referenced: ChatGPT, Total Computer Application(Morning Star)

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