java 类和对象 属性和行为 成员变量和局部变量

Posted 2022-12-06 DQ_CODING

概念

使用

案例

public class PersonText 
    public static void main(String[] args) 
        Person person = new Person();
        person.name = "dq";
        person.age = 11;
        person.eat("番茄炒蛋");
    


class Person 
    /**
     * 姓名
     */
    String name;
    /**
     * 年龄
     */
    Integer age;

    /**
     * 方法-吃饭
     */
    void eat(String lunch) 
        System.out.println(age + "岁的" + name + "吃" + lunch);
    

对象的内存解析1

案例1

public class PersonText 
    public static void main(String[] args) 
        Person person1 = new Person();
        person1.name = "dq";
        person1.age = 11;
        person1.eat("番茄炒蛋");

        Person person2 = new Person();
        person2.name = "dq2";
        person2.age = 112;
        person2.eat("番茄炒蛋2");

        Person person3=person1;
        person3.eat("3");
    


class Person 
    /**
     * 姓名
     */
    String name;
    /**
     * 年龄
     */
    Integer age;

    /**
     * 方法-吃饭
     */
    void eat(String lunch) 
        System.out.println(age + "岁的" + name + "吃" + lunch);
    

对象的内存解析2

案例

成员变量和局部变量

案例

详细

方法概念

分类

说明

return后面不写东西

方法注意点

案例1

package lesson.l10_oop;

/**
 * Illustration
 *
 * @author DengQing
 * @version 1.0
 * @datetime 2022/7/1 9:02
 * @function
 */
public class PersonDemo 
    public static void main(String[] args) 
        PersonObject person1 = new PersonObject();
        person1.name="tt";
        person1.age=30;
        person1.sex=1;
        person1.study();
        person1.addAge(2);
        person1.showAge();


        PersonObject person2 = new PersonObject();
        person2.name="oo";
        person2.age=18;
        person2.sex=2;
        person2.study();
        person2.addAge(2);
        person2.showAge();

    


class PersonObject 
    String name;
    int age;
    /**
     *1是男性
     * 2是女性
     */
    int sex;

    public void study() 
        System.out.println("studying");
    

    public void showAge() 
        System.out.println("age:" + age);
    

    public int addAge(int i) 
        this.age += i;
        return this.age;
    

案例2

package lesson.l10_oop;

/**
 * Illustration
 *
 * @author DengQing
 * @version 1.0
 * @datetime 2022/7/1 9:16
 * @function 计算圆的面积
 */
public class CircleText 
    public static void main(String[] args) 
        Circle circle = new Circle();
        circle.r = 0.5;
        System.out.println("圆的面积为" + circle.countArea());
    


class Circle 
    double r;

    public double countArea() 
        return Math.pow(r, 2) * 3.14;
    

案例3

package lesson.l10_oop;

/**
 * Illustration
 *
 * @author DengQing
 * @version 1.0
 * @datetime 2022/7/1 9:46
 * @function
 */
public class Method 
    public static void main(String[] args) 
        Method m=new Method();
        System.out.println("矩形的面积为："+m.method(10,8));
    
    public int method(int m,int n)
//        宽
        for (int i = 0; i < n; i++) 
//            长
            for (int j = 0; j < m; j++) 
                System.out.print("*\\t");
            
            System.out.println();
        
        return m*n;