title: Import customize package shows "error: package com does not exist"
body: <p>this is my file tree:</p>
  
  <pre><code>$ tree
  .
  ├── Hi.java
  ├── com
  │   └── libai688
  │       ├── User.class
  │       └── User.java
  </code></pre>
  
  <p>this is my Hi.java:</p>
  
  <pre><code>import com.libai688;
  
  public class Hi {
      public static void main(String[] args) {
          User p1 = new User();
      }
  }
  </code></pre>
  
  <p>while I am trying to compile Hi.java</p>
  
  <pre><code>$javac Hi.java
  Hi.java:1: error: package com does not exist
  import com.libai688;
            ^
  Hi.java:5: error: cannot find symbol
          User p1 = new User();
          ^
    symbol:   class User
    location: class Hi
  Hi.java:5: error: cannot find symbol
          User p1 = new User();
                        ^
    symbol:   class User
    location: class Hi
  3 errors
  </code></pre>
  
  <p>it throws a long error, I carefully check it with some other project, but I still can not find what is wrong with it.</p>
  
  <p>As I know, in some other language, if you want to import a customized module it should write a relative path. But in Java, I am confused with how to import a third-party module or a customized muddle.</p>
  
  <p>This is my User.java</p>
  
  <pre><code>package com.libai688;
  
  public class User{
      public String name;
      public int age;
      public User(String name, int age){
          this.name = name;
          this.age = age;
      }
  }
  </code></pre>