Chapter 3

Question 1

Abstraction

Answer 1

The ability to ignore details of parts to focus attention on a higher level of a problem

Question 2

modularization

Answer 2

Process of dividing a whole into well-defined parts which can be built and examined separately, and which interact in well defined ways

Question 3

Classes define ___

Answer 3

types. A class name can be used as the type for a variable. Variables that have a class as their type can store objects of that class.

Question 4

What are the 2 types in Java?

Answer 4

primitive and object types

Question 5

Primitive type

Answer 5

• stored directly in variable
• non-object type
• Types suchas int, boolean, char, ­double, and long are the most common primitive types.
• Primitive types have no methods.
• pre-defined in the java language

Question 6

object types

Answer 6

• not stored directly in variable but the reference of the object is stored (object references)
• defined by classes

Question 7

Internal method call

Answer 7

• no variable name required
• method is in the same class as the call of the method
• syntax:
  methodName(parameter-list)
  ie.
  updateDisplay();

Question 8

External method call

Answer 8

• method call to a method of another object using dot notation
• syntax:
  object.methodName(parameter-list)
  ie.
  minutes.increment();

Question 9

object.methodName(parameter-list)
this syntax is know as___

Answer 9

dot notation:
It consists of an object name, a dot, the method name, and parameters for the call

Question 10

name overloading

Answer 10

• the same name being used for 2 different entities.
• a class may contain more than one constructor, or more than one method of the same name, as long as each has a distinctive set of parameter types

Question 11

What keyword is used in the case of name overloading to refer to the field instead of the closest parameter?

Answer 11

“this” such as:
this.from

“this” refers to current object so this particular “this” refers to the “from” field in the current object.

Question 12

class diagram

Answer 12

• shows the classes of an application and the relationships b/t them
• gives info about the source code
• presents static view of a program

Question 13

object diagram

Answer 13

• shows the objects and their relationships at one moment in time during the execution of an application
• gives info about objects at runtime and presents the dynamic view of a program

Question 14

&&

Answer 14

Logical “and” operator that causes the condition in the if-statement to be true if both the conditions on either side of the “&&” symbol are true

Question 15

What are the 3 most important logical operators?

Answer 15

and, or and not

Question 16

II

Answer 16

“or” logical operator,
“a II b” is true if either a or b or both are true - false if they are both false

Question 17

!

Answer 17

“not” logical operator
- “! a” is true if a is false and false if a is true

Question 18

What would happen if one of the operands of a plus operation is a string and the other is not? as in :
“answer: “ + 42

Answer 18

If one of the operands of a plus operation is a string and the other is not, then the other operand is automatically converted to a string, and then a string concatenation is performed.
“answer: 42”

Question 19

What would be the result of this concatenation?
“Java” + “with BlueJ”

Answer 19

“Javawith BlueJ”
note: if you want a space, include it within one of the strings.

Question 20

What would the result of this be?
return “” + value;

Answer 20

“value”
If we concatenate “value” with an empty string, it will be converted to a string and no other characters will be prefixed to it.

Question 21

Object creation

Answer 21

• objects can create other objects, using the new operator
• syntax:
  new ClassName (parameter-list)
• new operation:
  1. creates a new object of the named class
  2. executes the constructor of that class

Question 22

debugger

Answer 22

• A software tool that helps in examining how an application executes.
• can be used to find bugs

Question 23

Breakpoint

Answer 23

• A flag attached to a line of source code that will stop the execution of a method at that point when it is reached.
• represented in the BlueJ editor as a small stop sign

Question 24

Primitive vs object types

Answer 24

Primitive
- predefined
- held in stack
- 2 distinct variables are overrated + 2 separate assignments. Values should be same
- do not null value as default value
- examples: byte, float, double, char, Boolean, etc

Object
- user-defined
- original object kept in the heap & ref variable kept in stack
- 2 ref variables are generated, both highlight similar article on the heap
- ref variable default value is null
- example: array, String etc