AP Computer Science A - Java Fundamentals

Front

What is the difference between a class and an object?

Back

A **class** is a blueprint or template for creating objects, defining attributes and behaviors. An **object** is a specific instance of a class with actual values for those attributes. Example: 'Dog' is the class; 'Fido' is the object.

Front

What are the 8 primitive types in Java?

Back

The 8 primitive types are: **int**, **double**, **boolean**, **char**, **long**, **short**, **byte**, and **float**. They store raw data values rather than references to objects.

Front

How is the `length()` method different from the `length` property?

Back

In Java, `length` is a property (field) of arrays, as in `arr.length`. `length()` is a method of the `String` class, as in `str.length()`.

Front

What does the `new` keyword do?

Back

The `new` keyword **instantiates** a class by allocating memory for a new object and calling the class's constructor to initialize that object. Example: `String s = new String("hello");`

Front

What is the scope of a local variable?

Back

A local variable is declared inside a method or a block of code (like inside a loop). It is **only accessible** within that specific method or block and ceases to exist when the method or block completes execution.