copyright © 2015 curt hill java for minecraft those things you should know

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Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

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Page 1: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Copyright © 2015 Curt Hill

Java for Minecraft

Those things you should know

Page 2: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Introduction

• As you know Minecraft is written in Java

• In order to create mods for Minecraft there are parts of the language that you may not know and should

• This presentation should start to cover much of this– Well that is the hope anyway

Copyright © 2015 Curt Hill

Page 3: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Topics

• General• Pointers• Final• Visibility• Annotations• Class definition• Inheritance and polymorphism

Copyright © 2015 Curt Hill

Page 4: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

General

• C++ and Java have much in common

• There is virtually no difference in:– Declarations and types– If– For– While– Do/while– Method calls

Copyright © 2015 Curt Hill

Page 5: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Exceptions

• Java uses boolean instead of bool• The conditional in if/for/while must

be a Boolean• The C/C++ scheme of zero is false,

everything else is true is not allowed

Copyright © 2015 Curt Hill

Page 6: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Visibility• C++ sets its visibility in sections• Java immediately prefixes any

declaration with the visibility:protected class helper{…}

• Any item without a visibility has “friendly” visibility– This makes it public to anything in the

same file and private to anything not in that file

• Every public class must be in a file of the same name

Copyright © 2015 Curt Hill

Page 7: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Preprocessor

• Java has no preprocessor • Thus it uses import instead of

include• Java also uses the package

statement instead of namespaces• Java has a larger role for final than

C++ does const

Copyright © 2015 Curt Hill

Page 8: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Final

• Java uses final instead of const• Thus a constant variable uses the

final declaration:final String VERSION = “1.1.4”;

• The final keyword may also be used in a class declaration:public final class some{…}– This indicates that no derivation may

be made of class some

Copyright © 2015 Curt Hill

Page 9: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Heap and Stack• C/C++ allows any type to be on

either the heap or stack• Java only allows primitives and

handles on the stack• All objects must be on the heap and

created with new• Java only allows dots and not the ->• Java does not allow delete, garbage

collection is the only way to claim unused heap memory

Copyright © 2015 Curt Hill

Page 10: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Pointers

• Java claims to have no pointers, it calls them handles instead– A handle is a restricted pointer

Copyright © 2015 Curt Hill

Page 11: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Annotations• Java annotations are a feature not

present in C/C++• Annotations given hints to the

compiler or run-time system• An annotation starts with the @

followed by a word which determines the type of annotation

• An annotation may be followed by a parenthesized list of parameters

• There are some standard Java annotations and some particular to Minecraft

Copyright © 2015 Curt Hill

Page 12: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Annotations Again

• @Override• @Mod • @Instance• @SidedMod• @EventHandler• Annotations are not terminated by

a semicolon

Copyright © 2015 Curt Hill

Page 13: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

@Override

• Standard Java annotation• Tells the compiler that the method

that follows overrides a method in the ancestral class

• If there is no method that this overrides a compile error occurs• Usually this is a misspelled the name

or made a mistake on the signature • The compile error prevents a run-time

or logic errorCopyright © 2015 Curt Hill

Page 14: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

@Mod

• Indicates to forge that this is the Base of a Mod class

• Three parameters:• modid – a unique ID for the mod• name – people readable name • version – the version

• All three are strings

Copyright © 2015 Curt Hill

Page 15: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

@Instance

• The instantiation of the mod class• What follows is usually a static

instance of the mod class • See the following example for

@Mod and @Instance

Copyright © 2015 Curt Hill

Page 16: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Example

• Here is some sample code:@Mod(modid = “CurtModID”,, name = “CurtMod”, version = “1.0.2”)public class CurtMod { …@Instancepublic static CurtMod instance = new CurtMod();

Copyright © 2015 Curt Hill

Page 17: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

@SidedMod• Announces which proxy is to be

loaded depending on whether a client or server is running– Precedes the declaration

• Two parameters:– clientProxy– serverProxy

• May not use anything but a literal string

• See next slide for example

Copyright © 2015 Curt Hill

Page 18: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Example

• Annotation and instance:@SidedProxy(serverSide= "edu.vscu.ServerProxy", clientSide= "edu.vscu.ClientProxy")public static CommonProxy proxy;

• CommonProxy was the ancestor of both ServerProxy and ClientProxy in this example

Copyright © 2015 Curt Hill

Page 19: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

@EventHandler

• Indicates that the method that follows will be an event handler

• Recall that event handlers are typically not called directly by code in the same file

• Instead called unpredictably by system code– In Minecraft’s case usually by the

Forge or Minecraft itself

Copyright © 2015 Curt Hill

Page 20: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Classes

• The class definition is slightly different than C++

• Inheritance and polymorphism are as well

• These we will cover in their own presentation

Copyright © 2015 Curt Hill

Page 21: Copyright © 2015 Curt Hill Java for Minecraft Those things you should know

Finally

• It is possible, even likely, that despite this presentation you will find features in mod code that are confusing

• Ask!

Copyright © 2015 Curt Hill