带你用Java全面剖析类和对象

目录

• 一、面向过程？面向对象？
• 二、类和类的实例化
  • 2.1普通成员变量和普通成员方法
  • 2.2 静态成员变量和静态成员方法
• 三、封装
  • 3.1 private
  • 3.2 getter 和 setter
• 四、构造方法
  • 4.1 基本语法
  • 4.2 this 关键字
• 五、代码块
  • 5.1 普通代码块
  • 5.2 构造代码块
  • 5.3 静态代码块
  • 5.4 注意事项
• 六、快捷方法
  • 6.1 toString方法
  • 6.2 setter / getter 方法
  • 6.3 构造方法（快捷）
• 总结

//创建一个类
class <类的名字> {
    field;//成员变量
    method;//成员方法
}
//实例化一个对象
<类的名字> <对象名> = new <类的名字>();

class Person {
    public int age;
    public String name;//成员变量放在对象当中，即堆上
    public void show() {
        //int a = 10;
        //a变量定义在方法中，它不是成员变量，是局部变量，在栈上开辟内存
        System.out.println("姓名: " + name + " 年龄: " + age);
    }
}
public class TestDemo {
    public static void main(String[] args) {
        Person person1 = new Person();
        person1.age = 18;
        person1.name = "富春";
        person1.show();
        Person person2 = new Person();
        person2.age = 21;
        person2.name = "山居";
        person2.show();
    }
}

class Person {
    public int age;
    public String name;
    public boolean ans;
    public char ch;
    public void show() {
        System.out.println("姓名: " + name + " 年龄: " + age);
        System.out.println("ans：" + ans + " ch：" + ch);
    }
}
public class TestDemo {
    public static void main(String[] args) {
        Person person = new Person();
        person.show();
    }
}

class Person {
    public int age;
    public static int count;
    public static final int COUNT = 99;
    //COUNT 是静态常量
    public static void staticTest() {
        System.out.println("这是静态成员方法");
    }
}
public class TestDemo {
    public static void main(String[] args) {
        Person person1 = new Person();
        person1.age = 18;
        Person.count = 20;
        System.out.println(person1.age + " " + Person.count);
        Person.staticTest();
    }
}

class Person {
    private int age;
    private String name;
    public int getAge() {
        return age;
    }
    public void setAge(int myAge) {
        age = myAge;
    }
    public void setName(String myMame) {
        name = myMame;
    }
    public String getName() {
        return name;
    }
    public void show() {
        System.out.println("姓名: " + name + " 年龄: " + age);
    }
}
public class TestDemo {
    public static void main(String[] args) {
        Person person1 = new Person();
        person1.setAge(18);
        person1.setName("富春");
        int age = person1.getAge();
        String name = person1.getName();
        System.out.println(name + " " + age);
        person1.show();
    }
}

class Person {
    private int age;
    private String name;
    public Person() {
        System.out.println("不带参数的构造方法");
    }
    public Person(String name) {
        this.name = name;
        System.out.println("带一个参数的构造方法");
    }
    public Person(String name,int age) {
        this.name = name;
        this.age = age;
        System.out.println("带两个参数的构造方法");
    }
    public void show() {
        System.out.println("姓名: " + this.name + " 年龄: " + this.age);
    }
}
public class TestDemo {
    public static void main(String[] args) {
        Person person1 = new Person();
        person1.show();
        Person person2 = new Person("富春");
        person2.show();
        Person person3 = new Person("山居",18);
        person3.show();
    }
}

class Person {
    private int age;
    private String name;
    public Person() {
        this("富春",18);//调用其他的构造方法
        System.out.println("不带参数的构造方法");
    }
    public Person(String name,int age) {
        this.name = name;
        this.age = age;
        System.out.println("带两个参数的构造方法");
    }
    public void show() {
        System.out.println("姓名: " + this.name + " 年龄: " + this.age);
    }
}
public class TestDemo {
    public static void main(String[] args) {
        Person person1 = new Person();
        person1.show();
    }
}

public class TestDemo {
    public static void main(String[] args) {
        int a = 10;
        {
            int b = 20;
            System.out.println(b);
        }
        System.out.println(a);
    }
}

class Person {
    private int age;
    private String name;
    {
        this.name = "山居";
        this.age = 18;
    }
    public void show() {
        System.out.println("姓名: " + this.name + " 年龄: " + this.age);
    }
}

class Person {
    private int age;
    private String name;
    public static int count;
    static {
        count = 20;
    }
    public void show() {
        System.out.println("姓名: " + this.name + " 年龄: " + this.age);
    }
}

class Person {
    public int age;
    public String name;
    @Override
    public String toString() {
        return "Person{" +
                "age=" + age +
                ", name="" + name + """ +
                "}";
    }
}
public class TestDemo {
    public static void main(String[] args) {
        Person person1 = new Person();
        person1.age = 18;
        person1.name = "富春";
        System.out.println(person1);
    }
}

class Person {
    private int age;
    private String name;
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
        //age = age;错误
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public void show() {
        System.out.println("姓名: " + name + " 年龄: " + age);
    }
}

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