Java: classes and objects use

In object-oriented programming, each object belongs to a class. In this practical tip we show you how to in Java classes and objects correctly can use.

Java: methods, programming

If you are using Java or have no experience you should, can you first of all, the Java-Basics reference. Various example programs we show them in the gallery at the end of the article.

In Java, the object-oriented programming ("OOP") is used. In this case, each object is independent and has its own unique identity ("identity"). In addition, each object characteristics ("attributes") and a specific behavior ("behavior has"). A class, in turn, describes (or defines) the objects.
In Java, there is a the methods, which define the behavior. A method is a collection of commands. An example of the Code "static void sayHello() {" ⮩ "System.out.println("Hello World");" ⮩ "}".
This method, you can call now, by inserting the command "sayHello();" in your main program.
You can also create methods with parameters. For example, the Code "static void sayHello(String name) {" ⮩ "System.out.println("Hello" + name);" ⮩ "}". You can now paste the command "sayHello("CHIP");" in the main program. The program would now write "Hello CHIP".
If you want to, you can create a method that returns a return value. The Code "static int sum(int val1, int val2) {" ⮩ "return val1 + val2;" ⮩ "}" for example, is the sum of two integers. The Keyword "void" has been omitted here, since the function has a return value.

Classes and objects in Java

In Java, classes and objects are easy to create. What you should have in mind, we have listed them here.

First of all, we create with the Code "public class Animal {" ⮩ "void bark() {" ⮩ "System.out.println("Woof-Woof");" ⮩ "}" ⮩ "}" a new class called "Animal", which contains the method "bark ()". In this class, you can access it from the Main class. For this, insert the Code "Animal dog = new Animal();" ⮩ "dog.bark();" in your Main class. The program would now "spend Woof-Woof". Here, dog," an object of type "is "Animal".
Similarly, you can also access a class variable to create, and of a different class from, or edit them.
At the beginning of each class, different Keywords are. Surely you've ever asked yourself, what is the meaning of this. The explanation is relatively simple. In the case of a class that any other class can access it, write at the beginning of "public". When "default" is a class for all other classes in the same Package available. A "protected"class is similar to a "default"class, with Subclasses, but the methods and variables of the Superclass can be viewed. Finally, there is the "private"class, which only has self-access.
In Java there are "Getters" and "Setters". With this, you'll easily values of variables and can change. An example of a Getter, the Code "public String getColor() {" ⮩ "return color;" ⮩ "}". This Code returns the value of the variable "color". An example of a Setter in the Code "public void setColor(String c) {" ⮩ "this is.color = c ;" ⮩ "}", which changes the value of the variable "color".
Also very practical are the "Constructors in Java". In doing so, you create a method which creates a Variable with a specific value. You can also use Getters and Setters.
In the Java Developement Kit (JDK) is included with the Math Class. With the command "Math.abs(-20);" you can have the amount of a number; in this case, the "20" would be. With "Math.ceil(7.234);" you can round a floating-point number to the next higher Integer. In this case, the is the number 8. With "Math.floor();" you can round off a floating-point number. Furthermore, you can use "Math.max(10, 20);" the higher the value of output. The opposite of this is "Math.min();". Finally, you can use the command "Math.pow(2, 3);" the number 2 with the number 3 potentiate. The result in this case is 8.
If you define a Variable or method as "static", it means that this Variable or method belongs to the class and not to a specific instance. Simply said, the existence of this object only once is called. So you can call a static method without creating a new object.
With the Keyword "final" can you make a Variable constant, so that it can not be changed. An example of the command is "public static final double PI = 3.14 is;".
To avoid conflicts due to different names, you can create in Java "Packages". A Package you can easily create in your Java IDE. This is a collection of similar classes. If you create a class within a package, it will appear the Code "package samples" at the beginning. A class within a package, you can, for example, with the command "import samples.Vehicle;" import.

Tips and Tricks for classes

So that you can work with classes even more efficient, we have some tips for you.

In Java there is the so-called data encapsulation, in the case of the data from the user and other classes are hidden. It is defined in Java, a Variable as "private" and "public" Getters and Setters to edit or view the variables provided.
Also, in Java there is the "inheritance". A class receives the properties (methods and variables) of another class to access. The class that receives these permissions is called a "Subclass". The other class is called "Superclass". To inherit from a class that uses the Keyword "extends". An example of the Code "class Dog extends Animal {is". This Dog is the Subclass, and "Animal" for the Superclass.
Furthermore, there is also a feature called polymorphism. In this case, each Subclass inherits for example, the properties of a Superclass, each Subclass has a method with the same name, which does, however, each Time something different.
If a Subclass defines a method that has these specific properties, it is called "Overriding". If methods have the same name but different parameters is called, the Whole "Overloading".
Very handy the abstraction in Java. An abstract method is a method, which is defined without implementation. An example of the Code "abstract void walk();". The actual method is now defined in a Subclass. If you want to access with a class on an abstract class, for example, with a "class cat extends Animal {".
In addition, you can create in Java "Interfaces". This is an abstract class that contains only abstract methods. Instead of "class Animal {" write at the beginning of the "interface Animal {". If you want to access with another class in this class, write you instead of "extends" but not "implements".
If you assign the value of a Variable of a certain type to another variable of a different type, called "Type Casting". After the command "int a = (int) 3.14;" the Variable "a" has the value "3". Similarly, you can also set an object ("instance") of a Subclass in a Superclass. An example of this is the command, "Animal a = new Cat () is;". This is called "Upcasting". However, there are also the "down-casting", wherein an object of a Superclass in a Subclass will be set. An example is the Code of "Animal a = new Animal();" ⮩ "((Cat)a).make sound();".
A method in Java also change while the program is running. To do this, write "@Override", and then define the method again.
In Java, a class can be part of another. For example, a public Class can contain a private Class.
Very practically, also, the equals method is. Here, an object is compared with another. If two variables (a1 & a2), for example, have the same value and data type is "System.out.println(a1 == a2);" nevertheless, "false", as these have the same location.
Finally, you should also know about Enums. This is a special type to define a collection of constants. The Code is "enum Rank {" ⮩ "SOLDIER," ⮩ "SERGEANT," ⮩ "CAPTAIN," ⮩ "}" defines a simple Enum. For example, you can use the command "Rank a = Rank.SOLDIER;" a constant "a" Deposit.

Java: Programming Guide Part 2

Once you now the Basics to classes, you can be our part 2 of the programming Guide to watch. There you will learn more about lists and Threads in Java.

In the next practical tip we will show you how to use a QR Code without a Scanner to decode can.