com.itbaizhan.oopTestExtends {
}

Person{
    String (){
        System..println()}
}

Student Person{
    String (){
        System..println()rest()System..println(.)}

    (String nameheightString major){
        .= name.= height.= major}
}

老师，不是说Stedent这个类继承了Persion这个类的方法和属性吗？为什么下面还要用构造函数赋值

老师去哪里下载你视频中讲到的这些安装包呀

这句话意思是不是说：接口不能创建接口类的实例，但是接口可以通过声明引用变量类型，从而引用实现类的对象？

class TestA implements A{
    @Override
    public void moren() {
        System.out.println("TestA.moren");
    }
}

为什么我敲 public class TestA implements A{} 会报错，删掉public就好了

老师，会出现这个效果是咋回事

sum = oddSum = evenSum = b = (b<=){
    sum +=bb++(b%==){
        evenSum +=b}{
        oddSum +=b}

这段代码，偶数和结果是2550，奇数和结果是2601，哪里出问题了？

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: Cannot invoke "com.bjsxt.Shell.drawMySelf(java.awt.Graphics)" because "this.shells[i]" is null

at com.bjsxt.MyGameFrame.paint(MyGameFrame.java:104)

at java.desktop/sun.awt.RepaintArea.paintComponent(RepaintArea.java:264)

at java.desktop/sun.lwawt.LWRepaintArea.paintComponent(LWRepaintArea.java:59)

at java.desktop/sun.awt.RepaintArea.paint(RepaintArea.java:240)

at java.desktop/sun.lwawt.LWComponentPeer.handleJavaPaintEvent(LWComponentPeer.java:1310)

at java.desktop/sun.lwawt.LWComponentPeer.handleEvent(LWComponentPeer.java:1191)

at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5056)

at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2324)

at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2780)

at java.desktop/java.awt.Component.dispatchEvent(Component.java:4827)

at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:775)

at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:720)

at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:714)

at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)

at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)

at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:97)

at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:747)

at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)

at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)

at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)

at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:744)

at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)

at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)

at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)

at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)

at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)

at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

2022-12-25 19:46:49.339 java[93394:8193097] TSM AdjustCapsLockLEDForKeyTransitionHandling - _ISSetPhysicalKeyboardCapsLockLED Inhibit

飞机这个可以运行,但是IDEA终端按键时报红字

l

老师，这个随便填可以吗、还是我弄错了，怎么办

1，老师，Java会默认导入java.lang包，请问这种导入的原理是什么？

2、在导入自己创建的包时，很清楚可以看到路径

但是在导入java.awt.*；的时候，右侧的文件夹中根本看不到java.awt下所有的类，请问这其中的原理是什么？

这是什么问题啊之前可以的，麻烦老师帮我看看

老师的源代码执行时，台球窗口关掉后还会在运行，并且报错，需要加什么代码可以 执行关闭窗口后退出程序

你好老师，我下的是2020.2.1的版本，请问到这里要选择什么？ 和视频的页面不太一样

这时出现了什么问题？

package com.company;
import java.util.Scanner;
import java.util.Scanner;

public class calculate {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);System.out.println("请输入你的月薪:");
        double mouth = sc.nextInt();
        double suodee = mouth-5000;
        double nasuie = 0;
        while (true){

            if (suodee<3000){
                System.out.println("你不需要交税");
            }else  if(suodee<=3000){
                nasuie = suodee*0.03;
                mouth -=nasuie;

            }else  if(suodee<=12000){
                nasuie = suodee*0.1-210;
                mouth -=nasuie;

            }else  if(suodee<=25000){
                nasuie = suodee*0.2-1410;
                mouth -=nasuie;

            }else  if(suodee<=35000){
                nasuie = suodee*0.25-2660;
                mouth -=nasuie;

            }else  if(suodee<=55000){
                nasuie = suodee*0.3-4410;
                mouth -=nasuie;

            }else  if(suodee<=80000){
                nasuie = suodee*0.35-7160;
                mouth -=nasuie;

            }else {
                nasuie = suodee*0.45-15160;
                mouth -=nasuie;
            }
            System.out.println("应纳税所得额："+suodee+"\t"+"你纳税："+nasuie+"\t"+"实际工资："+mouth);
            int cmd = sc.nextInt();
            if (cmd==66){
                System.out.println("计算下一位:");
                continue;
            }if (cmd==88){
                System.out.println("退出程序！");
                break;
            }
        }
    }
}

为啥我输入66重新计算下一位会把

System.out.println("应纳税所得额："+suodee+"\t"+"你纳税："+nasuie+"\t"+"实际工资："+mouth);

输出一遍呢

执行main方法为什么会打印两句“休息一会”？

public class Test03{
    public static void main(String[] args) {
        Student s = new Student("高淇",172,"Java");
        s.person.rest(); //s.rest();
        s.study();
    }
}
class Person {
    String name;
    int height;
    public void rest(){
        System.out.println("休息一会！");
    }
}
class Student /*extends Person*/ {
    Person person = new Person();
    String major; //专业

    public Student(String name, int height, String
            major) {
//天然拥有父类的属性
        this.person.name = name; //this.name = name;
        this.person.height = height; //this.height = height;
        this.person.rest();
        this.major = major;
    }

    public void study() {
        System.out.println("在尚学堂好好学习");
    }
}