"Small white Java Growth series"--Object-oriented Foundation

Today, the Java object-oriented knowledge point ~ in fact. Java can be successful in its development process. Very large part of the reason is its object-oriented thinking ~

1. Concept

Nowadays, object-oriented thinking. is not a new knowledge point, we know that today very many languages have object-oriented thinking, of course, we also know today is still very fire C language. In fact, it's a process-oriented language. Contains the recent period of time also appeared a lot of new ideas, than the aspect of the function, oriented to the distributed, oriented ... And so on a series of things, in fact, these are just a concept ~

In object-oriented. There are, in fact, three basic features:
• Encapsulation: To ensure that the external is not visible;
• Inheritance: Continue to carry forward the vast majority.
• Polymorphism: It belongs to change to change;

2. Classes and objects

Well, the concept is done. Let's talk about classes and objects.

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Class: A class is a set of common products, is the same kind of things concentrated expression.
Object: Is the embodiment of a personality, is the product of the individual.

This sentence is very important: A class is a template for an object. Object is an instance of a class

3. Definitions of classes in Java

There are two ways of defining classes in Java: public class and Class

· The class declared with the public class must be the same as the file name, assuming that classes declared with class can differ from the file name

· In a *.java file, there can be only one public class. But there are multiple class definitions at the same time.

· If you define a class, you need to capitalize the first letter of each word--conventions

For example, the definition in the People.java file here:

Package me.javen.oop;//Pack Name class Person {//define class string name;//define attribute int age;//define Property public void Say () {//define method SYSTEM.OUT.PR Intln ("123");}} public class People {//define class public static void Main (string[] args) {//define method}}

4. Using class-to-object in Java

So, how do you use the classes defined above?

Person person = null;//is declared in the stack memory, this process is called declaring the object person = new person ();//opening up the corresponding heap memory space, this process is called instantiating the object

In fact, can write a statement, generally in the development is also a bar ~

That is: person person = new person ();

This is to show that the memory structure is written in two articles.

See the following procedure:

public static void Main (string[] args) {//define method Person man = Null;person = new person ();//Use Properties in Class Person.name= "Mr. Rice";p er Son.age=24;person.say ();//usage}

This way, the basic use of classes and objects is complete.

To come down and introduce the construction method

5. Construction method

Definition: The method name defined in a class is the same as the class name. And no return value declaration method, called a constructor method.

Or see just the code: person = new person ();

In fact, in the new process, new is the default constructor for the person class.

Remember: in a class, assuming that there is no clear definition of a construction method, you will actively generate a non-participatory, do-nothing construction method. If a constructor is present in a class, you must use the defined construction method in the new procedure.

This sentence for small white, it may be a bit difficult to understand, the semicolon before the possible good understanding a little bit. The first half of the sentence can be understood by the person who participates. The second half of the sentence about using the construction method may be a bit difficult. In fact it is not difficult to see the following procedure:

See, no, the Java syntax check for Eclipse reports an error, which is a constructed method that does not define person (), and is defined in the person class as a constructor of person (String name, int age).

Of course, the construction method can define multiple ~

Class Person {//defines the String name;//defines the attribute int age;//defines the property public the person (String name, int age) {//defines two parameters for the construction method}public person (String name) {//Define a constructor method for a number of}public person () {//define no-constructor method}public void Say () {//define method System.out.println ("Name:" + name + ". Age: "+ Ages";}}

In this way, the construction method is said to be finished.

The following is the encapsulation.

6, encapsulation of

From the definition: encapsulation means that the definition inside the class is invisible to the outside.

The role is to protect the security of the data ~

What does it mean to be invisible to the outside?

Look at the code:

private String name; Define attribute private int age; Defining properties

There will be errors in the process, prompting for no permission access (not visible to the outside)

One of these forms is called encapsulation ~

So, how did the name and age properties come to the interview?

Package me.javen.oop;//Pack Name class Person {//define class private String name;//define Property private int age;//define Properties */* * Use setter and Gett for encapsulated properties Er method */public String getName () {return name;} public void SetName (String name) {this.name = name;} public int getage () {return age;} public void Setage (int.) {this.age = age;} Public Man (string name, int age) {//Define two parameters construction method}public person (string name) {////define a parameter constructor}public person () {//define non-constructor party Method}public void Say () {//define method System.out.println ("Name:" + name + ", Age:" + Ages);}} public class People {//define class public static void Main (string[] args) {//define method person person = Null;person = new person ();//Tim Add no-reference construction method//Set the value by setter method Person.setname ("Mr. Rice");p erson.setage ();p Erson.say (); Usage//Getter method Gets the value of the encapsulated property System.out.println ("Name:" + person.getname () + ", Age:" + person.getage ());}}

Note:

1. The property or method does not want to be interviewed externally. can use the Privatekeyword declaration;

2, in the development process. Assuming that it is not a special case, the properties defined in the Java class basically require a set encapsulation.

"Small white Java Growth series"--Object-oriented Foundation