Notes of Learning Java
This document is mainly used to summarize all the notes for me leaning java.
Terms and Common Tools
Grade is a build tool that used to build projects.
- To build a project means transforming the code into something that can be executed.
API is the collections of components used for building applets.
JavaFX is used to create graphical user interfaces for any platform.
AWT is Abstract Window Toolkit.
The version name of Java 8 matches the following pattern:
- $MAJOR.$MINOR.$SECURITY
After Java SE 10, the version numbers follow a $YEAR.$MONTH format. A new version of Java is released every six months.
The core of the Java ecosystem is the class. A class groups fields and methods.
All Object types are described in files with the *.java extension. Object types are organized in packages.
A package is a hierarchy of directories, with the Java object types on the last level.
A package is usually named by the following template:
- edu.upenn.cis.precise.continue[*]+
JARs: Java Archives
A library groups one or more JARs.
Any Java desktop application has a special method named main that has to be declared in a top-level class. This method is called by the JRE to run the Java program/application and it’s called the entry point.
Without the main method, a Java project is a collection of classes that are not runnable, cannot be executed, and cannot perform certain functions. It is like the ignition lock cylinder of a car.
Maven is a build automation tool used primarily for Java projects, like Gradle which is gaining ground.
Syntax is the set of programming rules that define how terms should be connected to produce an understanable unit of commincation.
Compact import statements:
- import static java.lang.Math.*;
Modifier:
- Access Modifiers - controls the access level
- (classes) public, default
- (attributes, methods, and constructors) public, private, default, protected
- Non-Access Modifiers - do not control access level, but provides other functionality
- (classes) final, abstract
- (Attributes, methods) final, static, abstract, transient, synchronized, volatile
Encapsulation:
- accessors - getters - getXXX()
- mutators - setters - setXXX()
Polymorphism:
- Overriding - run-time polymorphism
- Overloading - compile-time polymorphism
Abstraction is an Objective-Oriented Programming (OOP) principle that manages complexity.
Enum type is a special class type. It cannot be instantiated externally. An enum is by default final.
- Enums are the tools for you to limit the implementation of a class to a fixed number of instances.
What is the difference between an interface and an abstract class?
- An interface is not a class, but it does help create classes.
- An interface is fully abstract.
- It has no fields, only method definitions (skeletons).
- A class can implement an interface, and unless the class is abstract, it is forced to provide concrete implementations for them.
- Each method inside an interface is implicitly public and abstract.
- The only methods with concrete bodies in an interface are static methods and starting with Java 8, default methods.
- Interfaces that declare no method definitions are called marker interfaces and have the purpose to mark classes for specific purposes.
- The most renowned/known Java marker interface is java.io.Serializable, which makes objects that can be serialized (their state can be saved to a binary file).
- There are two types of interfaces:
- Normal interfaces
- Annotations
- The difference between abstract classes and interfaces, and when one or the other should be used, becomes relevant in the context of inheritance.
- Java supports only single inheritance.
- A class can only have one superclass.
- Using interfaces multiple inheritance is possible in Java, and that classes extend classes and implement interfaces.
Shortcuts
1. Intellij IDE
Double Shift -> Quick Search (Classes/Files/Symbols/Actions)
Command + Click any object type -> Open the code of the object class
