英文:
Using main class inside the package in java
问题
以下是翻译好的部分：
我试图运行文件Demo.java，该文件在同一个包中调用Protection类，但是出现了错误。
这是主类。
package p1;
// 在p1中实例化各个类。
class Demo {
public static void main(String args[]) {
Protection ob1 = new Protection();
//Derived ob2 = new Derived();
//SamePackage ob3 = new SamePackage();
}
}
这是我想在主类中使用的类。
package p1;
public class Protection {
public int n = 1;
private int n_pri = 2;
protected int n_pro = 3;
public int n_pub = 4;
public Protection() {
System.out.println("基础构造函数");
System.out.println("n = " + n);
System.out.println("n_pri = " + n_pri);
System.out.println("n_pro = " + n_pro);
System.out.println("n_pub = " + n_pub);
}
}
它给出了以下错误：
$ javac Demo.java
Demo.java:6: 错误: 找不到符号
Protection ob1 = new Protection();
^
符号: 类 Protection
位置: 类 Demo
Demo.java:6: 错误: 找不到符号
Protection ob1 = new Protection();
^
符号: 类 Protection
位置: 类 Demo
2 错误
错误: 编译失败
英文:
I am trying to to run the file Demo.java which is calling Protection class within the same package but it is giving error
This is the main class.
package p1;
// Instantiate the various classes in p1.
class Demo {
public static void main(String args[]) {
Protection ob1 = new Protection();
//Derived ob2 = new Derived();
//SamePackage ob3 = new SamePackage();
}
}
And this is the class that I want to use in the main class.
package p1;
public class Protection {
public int n = 1;
private int n_pri = 2;
protected int n_pro = 3;
public int n_pub = 4;
public Protection() {
System.out.println("base constructor");
System.out.println("n = " + n);
System.out.println("n_pri = " + n_pri);
System.out.println("n_pro = " + n_pro);
System.out.println("n_pub = " + n_pub);
}
}
It is giving this error:
$ javac Demo.java
Demo.java:6: error: cannot find symbol
Protection ob1 = new Protection();
^
symbol: class Protection
location: class Demo
Demo.java:6: error: cannot find symbol
Protection ob1 = new Protection();
^
symbol: class Protection
location: class Demo
2 errors
error: compilation failed
答案1
得分: 1
你应该使用 javac，而不仅仅是 java
当你使用命令 java 时，你可以执行一个文件，但只能执行该文件中的类。在这里，你有几个文件，所以你应该先编译它们，然后才能使用它们。
请执行以下步骤：
$ mkdir p1
$ mv Demo.java Protection.java p1/
# 编辑 p1/Demo.java，将 `class Demo` 改为 `public class Demo`
$ javac p1/*
$ java p1.Demo
这将会起作用，并且会产生以下结果：
base constructor
n = 1
n_pri = 2
n_pro = 3
n_pub = 4
英文:
You should use javac, not java only
When you use the command java, you can execute a file, but only the classes in that file. Here you have several files, so you should compile them in order to use them.
Do the following:
<!-- language-all: lang-bash -->
$ mkdir p1
$ mv Demo.java Protection.java p1/
# edit p1/Demo.java to change `class Demo` to `public class Demo`
$ javac p1/*
$ java p1.Demo
This worked and resulted in the following:
base constructor
n = 1
n_pri = 2
n_pro = 3
n_pub = 4
答案2
得分: 0
你可以尝试这样做：
- 在 p1 中打开命令提示符，使用命令
javac .\Demo.java .\Protection.java；然后你会看到生成了两个 .class 文件。 - 使用命令
cd ..，然后你会看到你的包p1。 - 使用命令
java p1.Demo，然后你会看到预期的输出。
英文:
You could try this:
- open cmd in p1, use
javac .\Demo.java .\Protection.java; then you can see two .class files generated - use
cd .., then you can see your packagep1 - use
java p1.Demothen you can see the expected output
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