主类无法识别Liber类？无参构造缺失报错求助

Hey there! Let's work through your two issues step by step:

Issue 1: Missing no-argument constructor #

The error about needing Liber() happens because once you define a custom constructor (your Liber(int i, String T, int VP)), Java stops providing the default no-argument constructor automatically. When you try to create an instance with new Liber();, the compiler can't find that constructor.

Fix options: #

1. Add a no-argument constructor to the Liber class
   This lets you use new Liber() as you originally tried. Also, I noticed a bug in your existing constructor—you're assigning the parameter T to the member variable Titulli backwards! Correct that too:

   package tipetnumerike;
   public class Liber {
       private int id;
       private String Titulli;
       private int VitiPublikimit;
   
       // Add no-argument constructor
       public Liber() {
           // Optional: Set default values if needed, e.g.
           // this.id = 0;
           // this.Titulli = "";
           // this.VitiPublikimit = 0;
       }
   
       public Liber(int i, String T, int VP) {
           id = i;
           VitiPublikimit = VP;
           Titulli = T; // Fixed the assignment direction here
       }
   
       // Complete the getId method
       public int getId() {
           return id;
       }
   }
   

2. Use your existing parameterized constructor
   If you don't need a no-argument constructor, pass the required values when creating the instance:

   // In your main method
   Liber l = new Liber(1, "My Book Title", 2023);
   

Issue 2: Main class can't recognize the Liber class #

This usually comes down to package structure or imports. Here's how to fix it:

If your main class is in the same package (tipetnumerike) #

• Make sure both Main.java and Liber.java are in the same directory (e.g., src/tipetnumerike/).
• Add the package declaration at the top of your main class:

  package tipetnumerike;
  import java.util.Scanner;
  
  public class Main {
      public static void main(String[] args) {
          Scanner s = new Scanner(System.in);
          Liber l = new Liber(); // Now this should work
      }
  }
  

If your main class is in a different package #

• Add an import statement for the Liber class at the top of your main class:

  import tipetnumerike.Liber;
  import java.util.Scanner;
  
  public class Main {
      public static void main(String[] args) {
          Scanner s = new Scanner(System.in);
          Liber l = new Liber();
      }
  }
  

• Also ensure your directory structure matches the package names (e.g., tipetnumerike/ folder containing Liber.java, and your main class in its own folder or root).

Compilation/Runtime tip #

If you're compiling from the command line, make sure to compile all files in the package:

javac tipetnumerike/*.java

Then run the main class using its fully qualified name:

java tipetnumerike.Main

内容的提问来源于stack exchange，提问作者alison