Good Constructors

Question 1

What are the two problems with common constructors?

Answer 1

1. Too many (optional) parameters

2. Magic numbers

Question 2

What are the four most common constructor techniques?

Answer 2

1. Builder
2. Static Factory Method
3. Telescoping
4. Java Bean

Question 3

How is the builder pattern implemented?

Answer 3

Public static inner class contains mandatory and. optional variables. Builder constructor with only mandatory parameters.

Question 4

How do you use a builder constructor?

Answer 4

A = new A.Builder(100,10)
.y(1)
.y(2)
.build();

Question 5

What are static methods?

Answer 5

An instance of the class needs to be created in order to call them.

Question 6

How do static factory methods work as a constructor?

Answer 6

Static methods return different instances of the class

Question 7

How are static factory methods implemented and used?

Answer 7

public static A newInstance(){
		return new A();
	}

A a = A.create();

Question 8

What are telescoping constructors?

Answer 8

Various constructors of different sizes. Smaller ones call the next bigger one.

Question 9

What is reflection in java?

Answer 9

A programm can examine a class definition and use it.

Question 10

How are JavaBeans used as a constructor?

Answer 10

1. Create empty object with constructor

2. set parameters with setters

Question 11

When would you use a builder and when a static factory method?

Answer 11

Builder: > 5 Parameters
SFM: < 5 Parameters