如何修复 java 中的流布局错误？

Question

I don't know why but I get an error everythime I run this code.

The error is: Exception in thread "main" java.lang.Error: Unresolved compilation problem: The method setLayout(LayoutManager) in the type JFrame is not applicable for the arguments (FlowLayout) at gui.FlowLayout.main(FlowLayout.java:14)

I'm learning Java and I'm a beginner so I don't really know what to do. Please help me.

package gui;

import java.awt.LayoutManager;
import javax.swing.JButton;
import javax.swing.JFrame;

public class FlowLayout {

    public static void main(String[] args) {
        
        JFrame frame = new JFrame(); //cerates frame
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //exit out of application
        frame.setSize(500, 500); //sets x-dimesion, and y-dimension of frame
        frame.setLayout(new FlowLayout());
        
        frame.add(new JButton("1"));
        frame.setVisible(true);
    }

}

Answer 1

There is a potential conflict between the class you created gui.FlowLayout and java.awt.FlowLayout , the layout you have to give to your frame.

The error is due to the fact the JFrame.setLayout() method expects a java.awt.FlowLayout and not a gui.FlowLayout which is the only FlowLayout available in your code.

To fix that, I'd do the following

1. Remove the ambiguity by renaming the class you created (to FlowLayoutExample for example).
2. Import the java.awt.FlowLayout you actually need.

The code should become:

package gui;
import javax.swing.JButton;
import javax.swing.JFrame;
import java.awt.FlowLayout;

public class FlowLayoutExample {

    public static void main(String[] args) {

        JFrame frame = new JFrame(); //cerates frame
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //exit out of application
        frame.setSize(500, 500); //sets x-dimesion, and y-dimension of frame
        frame.setLayout(new FlowLayout());

        frame.add(new JButton("1"));
        frame.setVisible(true);
    }
}

Note: there is also another possibility: you can skip the import and directly mention the complete class name (with the package):

frame.setLayout(new java.awt.FlowLayout());

I tend to prefer the first solution because:

• The name FlowLayout doesn't reflect what your class does while FlowLayoutExample is IMHO more explicit.
• Always using complete class names makes your code more verbose and thus less readable.

Answer 2

Just add the library: import java.awt.FlowLayout