Defining Data: Types, Variables and Classes

What Defining Data: Types, Variables and Classes covers

Defining Data: Types, Variables and Classes is examined in Unit AS 1, Introduction to Object Oriented Development — a written examination. It covers primitive types and their storage, reference types, objects and null, declaring variables, scope and lifetime, type casting and conversion, arithmetic operators and expressions, relational and logical operators, operator precedence and evaluation order, objects as occurrences of a class, abstract, base and inherited classes, attributes and the properties of a class, static variables in a class and interfaces and class reusability.

The 12 subtopics

Each one has its own page.

• Primitive types and their storageThe integer, floating point, character and boolean types, how many bits each occupies, the range each can hold, and what happens when a value exceeds it.Open →
• Reference types, objects and nullReference type, value null and wrapper class.Open →
• Declaring variables, scope and lifetimeScope of a variable and variable shadowing.Open →
• Type casting and conversionType casting and lost in a narrowing conversion.Open →
• Arithmetic operators and expressionsThe five arithmetic operators, integer against floating point division, the remainder operator and the sign it takes, increment and decrement in prefix and postfix form, and compound assignment.Open →
• Relational and logical operatorsValue does a relational expression produce and short-circuit evaluation.Open →
• Operator precedence and evaluation orderOperator precedence and value of true || false && false.Open →
• Objects as occurrences of a classSaying that an object is an occurrence of a class, term for creating an object from a class and state of an object.Open →
• Abstract, base and inherited classesBase class, inherited class and abstract class.Open →
• Attributes and the properties of a classAttribute of a class, saying that attributes represent the properties of a class and instance attribute.Open →
• Static variables in a classStatic variable, static constant and static method.Open →
• Interfaces and class reusabilityMain differences between an interface and an abstract class, one interface implemented by several unrelated classes and programming to an interface rather than to an implementation.Open →

What you need to know

Answer each one before you reveal it.

Take Defining Data: Types, Variables and Classes further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Abstract class vs Interface

  Abstract class: a type that may hold data and completed methods and can head only a single line of descent. Interface: a type that declares behaviour only, and any number of which may be promised by one implementer.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is a primitive data type?

   Model answer

   A primitive data type is a type built into the language whose variable holds the value itself, rather than holding a reference to an object stored elsewhere.

2. 2

   Which four integer primitive types does Java provide, and how wide is each?

   Model answer

   Java provides byte at 8 bits, short at 16 bits, int at 32 bits and long at 64 bits.

3. 3

   What range of values can a signed 8-bit integer hold, and how does that range follow from the number of bits?

   Model answer

   Eight bits give 256 different patterns, and in a signed type half are used for negative values, so the range runs from −128 to 127.

4. 4

   How many different values can be stored in 16 bits?

   Model answer

   Sixteen bits give 65 536 different values, because each extra bit doubles the number of patterns available.

5. 5

   Which two primitive types hold real numbers in Java, and which of the two is the more precise?

   Model answer

   Java holds real numbers in float at 32 bits and double at 64 bits, and double is the more precise, keeping roughly fifteen significant figures against roughly seven.

6. 6

   What values may a boolean variable hold, and how much information does a boolean actually carry?

   Model answer

   A boolean variable holds either true or false, so a boolean carries one bit of information even though a machine usually reserves a whole byte for it.

What is inside Levo

Six ways to work the same material.

Defining Data: Types, Variables and Classes revision questions

What does Defining Data: Types, Variables and Classes cover in CCEA A-Level Software Systems Development?

12 subtopics: primitive types and their storage, reference types, objects and null, declaring variables, scope and lifetime, type casting and conversion, arithmetic operators and expressions, relational and logical operators, operator precedence and evaluation order, objects as occurrences of a class, abstract, base and inherited classes, attributes and the properties of a class, static variables in a class and interfaces and class reusability. Each one has its own page with questions and model answers.

How is Defining Data: Types, Variables and Classes organised?

By the CCEA CL4 specification, subtopic by subtopic, so it matches the order you are taught it in.