VS Code 调试无法解析导入语句中的类，但使用命令行可以正常工作

Question

I'm working on some simple Data structures using Java and I'm using Princeton's library to implement the data structures but VS Code can't pick the files used under the import statements while it works fine if I compile and run the programs from the terminal.

Here's my Java code with comments depicting the situation:

//these imports work fine
import java.util.Iterator;
import java.util.NoSuchElementException;

//this is available in my local directory
    //VS code is unable to resolve these imports, however it works fine while using integrated terminal
    import edu.princeton.cs.algs4.Bag;
    import edu.princeton.cs.algs4.StdIn;
    import edu.princeton.cs.algs4.StdOut;


public class Stats {
    public static void main(String[] args) {

        // read in numbers
        Bag<Double> numbers = new Bag<Double>();

        int i = 0;
        while (i < args.length) {
            numbers.add(Double.parseDouble(args[i]));
            i++;
        }
        int n = numbers.size();

        // compute sample mean
        double sum = 0.0;
        for (double x : numbers)
            sum += x;
        double mean = sum / n;

        // compute sample standard deviation
        sum = 0.0;
        for (double x : numbers) {
            sum += (x - mean) * (x - mean);
        }
        double stddev = Math.sqrt(sum / (n - 1));

        StdOut.printf("Mean:    %.2f\n", mean);
        StdOut.printf("Std dev: %.2f\n", stddev);
    }
}

Here's what I receive in VS Code build errors:

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
    StdOut cannot be resolved
    StdOut cannot be resolved

can someone please help me with this? I'm using Java Extension Pack from Microsoft

Answer 1

Any IDE that is supposed to compile or run Java code needs to have the required classes available. In other words:

1. learn what class path means in Java.
2. setup your IDE to know about all the 3rd party libraries/classes you intend to use, see the corresponding documentation for example.

Answer 2

To add to GhostCat's answer (I am doing the same Coursera class from Princeton), this piece of information is helpful:

https://code.visualstudio.com/docs/java/java-project

Tl;dr: I had to add this to my .classpath file in the vscode project directory:

<classpathentry kind="lib" path="/path_to_stdlib.jar" />

Answer 3

You can use maven to track all the dependence and then use the Maven for Java Extension which keep the track of pom.xml file changes and import the library in the project.

ref: https://code.visualstudio.com/docs/java/java-build