Java：从库访问用户生成的代码

Question

I am making a Library for my pupils to create a GUI easy in Java, but if they press a button in the Interface it should run a method created by them.
Is there any way to do this? I am not really into Java, but the curriculum wants me to:(

Answer 1

You can use reflection to run their class without requiring they implement an interface although you would still have to provide instructions to limit the argument types. This works only for methods with no arguments.

java.awt.EventQueue.invokeLater(() -> {
    JFrame frm = new JFrame();
    JPanel pnl = new JPanel();
    frm.add(pnl);
    pnl.setLayout(new BoxLayout(pnl, BoxLayout.Y_AXIS));
    pnl.add(new JLabel("Class"));
    JTextField classField = new JTextField();
    pnl.add(classField);
    pnl.add(new JLabel("Method"));
    JTextField methodField = new JTextField();
    pnl.add(methodField);
    JTextArea area = new JTextArea();
    area.setPreferredSize(new Dimension(300, 300));
    JButton btn = new JButton("Run");
    pnl.add(btn);
    pnl.add(area);
    System.setOut(new PrintStream(new OutputStream() {
        @Override
        public void write(int b) throws IOException {
            area.append(new String(new byte[]{(byte) b}));
        }
    }));
    btn.addActionListener(e -> {
        try {
            Class cls = Class.forName(classField.getText());
            Method m = null;
            Method ma[] = cls.getDeclaredMethods();
            String methodName = methodField.getText().trim();
            m = cls.getMethod(methodName,new Class[]{});
            Object o = cls.newInstance();
            Object mr = m.invoke(o);
            if(null != mr) {
                area.append("\nreturned "+mr.toString()+"\n");
            }
        } catch (Exception ex) {
            ex.printStackTrace();
            area.append("\nException "+ex.getMessage()+"\n");
        }
    });
    frm.pack();
    frm.setVisible(true);
});

given a class like:

public class StudentClass {
    public void print10() {
        int sum= 0;
        for(int i = 0; i< 10; i++ ) {
            System.out.println("i = "+i);
            sum+=i;
        }
    }
}

The fields would be need to be filled with StudentClass and print10 and the compiled class needs to be on your classpath.

Perhaps a better option would be to teach Processing ( https://processing.org/ ). This is essentially java since the Processing code gets pasted into a java class behind the scenes but is much more oriented to get beginners drawing graphical sketches. I guess you'd have to ask your administration if they would go for it and at some point the students would need to be able to write the code the processing tools are generating for them.