AP Computer Science A — 1) Using Objects and Methods (Deep Study Notes)

Object

A bundled package of data and behavior in Java, consisting of state and methods.

Class

A blueprint that defines the state (data) and methods (behavior) for objects of that type.

Java API

A collection of prewritten classes and methods that Java provides for developers.

Reference Type

A type in Java (like String) that stores a reference to an object, not the object itself.

Null

A literal representing 'no object' and can be assigned to any reference variable.

NullPointerException

An exception thrown when a method is called on a null reference.

Constructor

Special code that runs when an object is created, used to initialize the object.

Overloading

Defining multiple constructors or methods with the same name but different parameter lists.

Method Signature

The combination of a method's name, parameters, and return type.

Void Method

A method that performs an action without returning a value.

Non-Void Method

A method that produces a value when called.

Instance Method

A method that is called on an object instance.

Static Method

A method that is called on a class rather than an object.

Method Chaining

Calling multiple methods on an object in a single statement.

Wrapper Class

A class that encapsulates a primitive data type into an object, e.g., Integer wraps int.

Autoboxing

The automatic conversion of a primitive type to its corresponding wrapper class.

Unboxing

The automatic conversion of a wrapper class to its corresponding primitive type.

Math Class

A class in Java providing common mathematical operations and constants.

Math.random()

A method that returns a double value greater than or equal to 0.0 and less than 1.0.

String Immutability

A property of String objects in Java meaning they cannot be changed after creation.

IndexOf Method

A method that returns the index of the first occurrence of a substring within a string, or -1 if not found.

Equals Method

A method used to compare the contents of two strings for equality.

CompareTo Method

A method that compares two strings lexicographically and returns an int indicating the result.