Globalcode – Open4education

Trilha – Android

Bruno Fernandes CamposDesenvolvedor Mobile

EFFECTIVE JAVA

Globalcode – Open4education

About

Globalcode – Open4education

Why?

Globalcode – Open4education

How?

Globalcode – Open4education

Agenda

• What the difference in performance between for loops?

• How to deal with several parameters classes?• How to make static classes safe?• How to avoid the unecessary objects creation?

• Inside classes• Inside for loops• When concatenating strings

Globalcode – Open4education

Comparing For Loops

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For Loops In Arrays

Manual for-loop x Enhanced for-loop

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For Loops In Arrays

Manual for-loop x Enhanced for-loop

SAME PERFORMANCEWHEN READING ENTRANCES

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For loops in CollectionsFor each X Iterator

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For loops in CollectionsFor each X Iterator

SAME PERFORMANCE

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For loops in ArrayListsManual for-loop X For each

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For loops in ArrayLists

X For eachManual for-loop

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For loops in ArrayLists

X

1061 ms 1183 ms

For each

100000 strings logged in the console performance test

Manual for-loop

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Many Constructors Parameters

What should I do?

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Nutrition Facts Class

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Telescoping Pattern

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Using Telescoping Constructor Pattern

● Force some unwanted values● It does not scale well!● Parameters reversion

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Javabeans Pattern

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Javabeans Pattern

● Easy to read● Precludes the possibility of making a class imutable● Imutability -> "All of the information contained in each instance is

provided when it is created and is fixed for the lifetime of the object"

Globalcode – Open4education

The builder pattern!

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Using Builder Pattern

● Easy to read and Write● Safe -> Imutable

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How to turn static classes safe

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Static class

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AndroidAPIUtils Usage

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Wrong usage

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AndroidAPIUtils avoiding instantiability

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Avoid Creating Unecessary Objects

Globalcode – Open4education

Prefeer Static Factory Methods

Constructors will always create a new instance!

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INSIDE CLASSES

Avoid Creating Unecessary Objects

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Bad example

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Use Static initializers

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Why use static initialisers?● Calendar, Date and Timezone

instances created only once

● Executing 10 milion times : ○ 1st version took 32000ms○ 2nd version took 130 ms

250 times faster!

Globalcode – Open4education

INSIDE FOR LOOPS

Avoid Creating Unecessary Objects

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Bad practice at for loops

Globalcode – Open4education

Good allocation example

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WHEN CONCATENATING STRINGS

Avoid Creating Unecessary Objects

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Bad Practice

Globalcode – Open4education

Bad Practice

● Strings are immutable● Complexity square n

Globalcode – Open4education

Good Practice

● Linear complexity● 85 times faster than the first one for 8.000 strings.

Globalcode – Open4education

QUESTIONS?

This is the END