A package in Java is used to group related classes. Think of it as a folder in a file directory. We use packages to avoid name conflicts, and to write a better maintainable code. Packages are divided into two categories:
The meaning of Encapsulation, is to make sure that “sensitive” data is hidden from users. To achieve this, you must:
privateprivate variableYou learned from the previous chapter that private variables can only be accessed within the same class (an outside class has no access to it). However, it is possible to access them if we provide public get and set methods.
The get method returns the variable value, and the set method sets the value.
Syntax for both is that they start with either get or set, followed by the name of the variable, with the first letter in upper case: Continue reading Java Encapsulation
By now, you are quite familiar with the public keyword that appears in almost all of our examples:
public class Main
The public keyword is an access modifier, meaning that it is used to set the access level for classes, attributes, methods and constructors.
We divide modifiers into two groups:
A constructor in Java is a special method that is used to initialize objects. The constructor is called when an object of a class is created. It can be used to set initial values for object attributes: Continue reading Java Constructors
You learned from the Java Methods chapter that methods are declared within a class, and that they are used to perform certain actions:
Create a method named myMethod() in Main:
public class Main {
static void myMethod() {
System.out.println("Hello World!");
}
}myMethod() prints a text (the action), when it is called. To call a method, write the method’s name followed by two parentheses () and a semicolon; Continue reading Java Class Methods
In the previous chapter, we used the term “variable” for x in the example (as shown below). It is actually an attribute of the class. Or you could say that class attributes are variables within a class:
Create a class called “Main” with two attributes: x and y:
public class Main {
int x = 5;
int y = 3;
}
Another term for class attributes is fields.
Java is an object-oriented programming language.
Everything in Java is associated with classes and objects, along with its attributes and methods. For example: in real life, a car is an object. The car has attributes, such as weight and color, and methods, such as drive and brake.
A Class is like an object constructor, or a “blueprint” for creating objects.
OOP stands for Object-Oriented Programming.
Procedural programming is about writing procedures or methods that perform operations on the data, while object-oriented programming is about creating objects that contain both data and methods.
Object-oriented programming has several advantages over procedural programming:
Recursion is the technique of making a function call itself. This technique provides a way to break complicated problems down into simple problems which are easier to solve.
Recursion may be a bit difficult to understand. The best way to figure out how it works is to experiment with it.
In Java, variables are only accessible inside the region they are created. This is called scope.
Variables declared directly inside a method are available anywhere in the method following the line of code in which they were declared:
public class Main { public static void main(String[] args) { // Code here CANNOT use x int x = 100; // Code here can use x System.out.println(x);}}