[Java Object Exploration Journey]

Preface: Java is an object-oriented programming language, in which objects are data structures with state and behavior. By understanding Java objects, we can better grasp how to write high-quality, maintainable Java programs. This article will take you to deeply explore the world of Java objects and discuss the basic knowledge of Java objects, including what objects are, how to create objects, and how to use objects, etc., through some easy-to-understand examples and code samples to help you better understand and application Java objects.​ 

 

introduce

In computer science, an object is an instantiated class that encapsulates data and methods for manipulating that data. A class is an abstract description of a group of related objects that defines their state (i.e. properties) and behavior (i.e. methods). In Java, all objects must belong to a class.

For example, we might have a class calledCar that has states such as color, brand, and year, and behaviors such as driving, braking, and accelerating. A specific car instance is an object that has all the properties and methods of theCarclass.

public class Car {
    private String color;
    private String brand;
    private int year;

    public void drive() {
        // ...
    }

    public void brake() {
        // ...
    }

    public void accelerate() {
        // ...
    }
}

In this example, the Car class represents a car in a general sense, and an instance of Car is a specific car, such as A red BMW 2020 car.

Create object

In Java, we have two ways to create objects: using the new keyword or using the reflection API.

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This is the most common way to create objects:

Car car = new Car();

This code first declares a variable named car, and then uses the new keyword to create a new Carobject and assign it tocarvariable.

Use reflection API

The reflection API allows us to dynamically create objects at runtime. This approach is often used in advanced applications that require flexibility and complexity:

Class<Car> clazz = Car.class; Car car = clazz.newInstance();

This code first obtains the Class object of the Car class, and then calls its newInstance() method to create a new CarObject.

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Once the object is created, we can access its properties and methods.

Access properties

We can access the properties of an object through the dot operator:

car.color = "red"; System.out.println(car.brand);

This code first sets the color of car to "red", and then prints out the brand of car.

call method

We can also call methods on objects:

car.drive(); car.brake(); car.accelerate();

This code calls car's drive(), brake() and accelerate() respectively method.

Example

Next we will show how to create and use Java objects through some practical examples.

Create and use simple objects

public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public void introduce() {
        System.out.println("Hi, my name is " + name + ", and I am " + age + " years old.");
    }
}

Person person = new Person("Tom", 20);
person.introduce(); // 输出: Hi, my name is Tom, and I am 20 years old

In this code, we first define a Person class, and then create a new Person objectperson and set his name and age. Finally, we called the method of person and output his self-introduction. introduce()

Create and use complex objects

public class Dog {
    private String name;
    private int age;
    private boolean isGoodBoy;

    public Dog(String name, int age, boolean isGoodBoy) {
        this.name = name;
        this.age = age;
        this.isGoodBoy = isGoodBoy;
    }

    public void bark() {
        System.out.println(name + " barked!");
    }
}

Dog dog = new Dog("Rex", 5, true);
dog.bark(); // 输出: Rex barked!

In this example, we create a classDog that has three attributes: name, age, and whether he is a good boy. We also define a bark() method that allows the dog to bark.

There are two special methods in Java: construction method and destruction method.

Constructor and Destructor A constructor is a special method that is called when an object is created. The name of the constructor is the same as the class name and has no return type. Below is an example:

class Person {
    String name;
    int age;

    Person(String name, int age) { // 构造方法
        this.name = name;
        this.age = age;
    }
}

The destructor method is a method called when the object is destroyed, and it can release resources. The destructor method in Java is implemented using the keyword finally. Here's an example:

class Person {
    String name;
    int age;

    Person(String name, int age) { // 构造方法
        this.name = name;
        this.age = age;
    }
}

Summarize

Java objects are one of the core concepts of Java programming. Understanding and mastering how to create and use Java objects is an important part of learning Java. I hope this article can help you better understand the concepts and usage of Java objects.