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Objects and Classes — Class 11 ISC Computer Science revision notes

A 3-page visual revision sheet for Objects and Classes, written for Class 11 ISC Computer Science. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.

Page 1 as PDF

Objects and Classes in one look

one blueprint, many separate things built from it

A class is a blueprint, an object is a thing built from it

• a class is a template that names a group of fields (its data) and methods (what it can do), written once
• an object is one actual thing built from that template while the program runs, also called an instance
• every object made from the same class has the same fields and the same methods, but each object holds its own separate values in those fields
• changing one object's fields never touches another object of the same class, since each has its own copy of the data

Fields and methods, the two things a class declares

• fields are also called instance variables: each object gets its own copy the moment it is built
• methods are the actions an object can perform, usually written to read or change that object's own fields
• a field is declared with a type and a name, the same way any variable is, just written inside the class body rather than inside a method
• a method is written with a return type, a name and a parameter list, and its own body of statements

What new does, step by step

1. new Car()
2. constructor runs
3. reference returned

A reference variable against a primitive variable

Primitive variable

• holds the actual value itself, such as an int holding 7
• copying it copies the value, and the two variables are independent afterwards

Reference variable

• holds the location of an object, never the object's fields directly
• copying it copies the location, so both variables then point at the same one object

Page 1 of 3. The full sheet, all 3 pages, opens free in the app.

What this Objects and Classes sheet covers

• A class is a blueprint, an object is a thing built from it
• Fields and methods, the two things a class declares
• What new does, step by step
• new Car()
• constructor runs
• reference returned
• A reference variable against a primitive variable
• Primitive variable
• Reference variable
• The new keyword builds an object
• The this keyword
• Words the question will use
• Traps that cost marks
• Tricks that save time

Open the full Objects and Classes sheet →Free, works offline, no account needed. All 3 pages, plus a study plan built around your own exam dates.

How CapCompass uses this sheet

These notes are not a standalone PDF. CapCompass plans Computer Science chapter by chapter against your real exam dates and free hours, and when the plan reaches Objects and Classes the sheet opens inside the study block itself — at the page covering the sub-topic that block is on, with the timer still running. Revision arrives at the moment the plan says revise, instead of having to be gone looking for.

More Computer Science Class 11 revision notes

• Arrays and Strings
• Basic Input Output and File Handling
• Encodings
• Implementation of Algorithms
• Introduction to Object Oriented Programming using Java
• Methods and Constructors
• Numbers
• Packages
• Primitive Values, Wrapper Classes and Types
• Propositional Logic and Hardware Implementation
• Recursion
• Statements and Scope
• Trends in Computing and Ethical Issues
• Variables and Expressions