如何在java程序中编译和运行

我想用另一个Java程序打开一个Java GUI。
它成功编译，但无法运行。 它说“无法加载主类”。 这是我的代码：

import javax.tools.JavaCompiler; import javax.tools.ToolProvider; public class Test { public static void main(String[] args) { try { JavaCompiler jc = ToolProvider.getSystemJavaCompiler(); jc.run(System.in, System.out, System.err, "src/HelloWorld.java"); // I think this line has the error Runtime.getRuntime().exec("cmd.exe /c start java src/HelloWorld"); } catch (Exception e) { e.printStackTrace(); } } } 

HelloWorld类：

 import javax.swing.JFrame; public class HelloWorld { public static void main(String[] args) { JFrame frame = new JFrame(); frame.setSize(100, 500); frame.setVisible(true); frame.setResizable(false); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } } 

Answer 1

您的代码可能会失败的任何数量的可能位置，例如，由于某种原因它可能无法编译; java可能不在OS的搜索路径中; java命令可能会失败，因为src/HelloWorld参数看起来不对。

我相信你的命令应该看起来更像java -cp ./src HelloWorld或者它应该在src目录的上下文中执行…

您确实需要尽一切努力来诊断潜在问题，例如JavaCompiler的DiagnosticCollector以及读取进程InputStream和ErrorStream

根据您的HelloWorld.java和之前的回答，我能够生成这个示例，它可以成功编译并运行您的类…

 import java.io.File; import java.io.IOException; import java.io.InputStream; import java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.logging.Level; import java.util.logging.Logger; import javax.tools.Diagnostic; import javax.tools.DiagnosticCollector; import javax.tools.JavaCompiler; import javax.tools.JavaFileObject; import javax.tools.StandardJavaFileManager; import javax.tools.ToolProvider; public class TestCompile { public static void main(String[] args) { StringBuilder sb = new StringBuilder(64); try { DiagnosticCollector diagnostics = new DiagnosticCollector<>(); JavaCompiler compiler = ToolProvider.getSystemJavaCompiler(); try (StandardJavaFileManager fileManager = compiler.getStandardFileManager(diagnostics, null, null)) { // >>>> Compiler Stage // This sets up the class path that the compiler will use. // I've added the .jar file that contains the DoStuff interface within in it... List optionList = new ArrayList<>(); optionList.add("-classpath"); optionList.add(System.getProperty("java.class.path")); Iterable compilationUnit = fileManager.getJavaFileObjectsFromFiles(Arrays.asList(new File("src/HelloWorld.java"))); JavaCompiler.CompilationTask task = compiler.getTask( null, fileManager, diagnostics, optionList, null, compilationUnit); if (task.call()) { // <<<< Compiler Stage // >>>> Run stage... ProcessBuilder pb = new ProcessBuilder("java", "-cp", "./src", "HelloWorld"); pb.redirectError(); Process p = pb.start(); InputStreamConsumer.consume(p.getInputStream()); p.waitFor(); // <<<< Run Stage } else { for (Diagnostic diagnostic : diagnostics.getDiagnostics()) { System.out.format("Error on line %d in %s%n", diagnostic.getLineNumber(), diagnostic.getSource().toUri()); } } } catch (InterruptedException ex) { Logger.getLogger(TestCompile.class.getName()).log(Level.SEVERE, null, ex); } } catch (IOException exp) { exp.printStackTrace(); } } public static class InputStreamConsumer implements Runnable { private InputStream is; public InputStreamConsumer(InputStream is) { this.is = is; } public InputStream getInputStream() { return is; } public static void consume(InputStream is) { InputStreamConsumer consumer = new InputStreamConsumer(is); Thread t = new Thread(consumer); t.start(); } @Override public void run() { InputStream is = getInputStream(); int in = -1; try { while ((in = is.read()) != -1) { System.out.print((char)in); } } catch (IOException exp) { exp.printStackTrace(); } } } } 

作为使用ProcessBuilder pb = new ProcessBuilder("java", "-cp", "./src", "HelloWorld");的替代方法ProcessBuilder pb = new ProcessBuilder("java", "-cp", "./src", "HelloWorld"); ，你真的可以用……

 ProcessBuilder pb = new ProcessBuilder("java", "HelloWorld"); pb.directory(new File("src")); pb.redirectError(); Process p = pb.start(); 

这将在src目录的上下文中启动java进程