呵呵，试一下。

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import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.io.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.border.*;

public class Test {
	public static void main(String[] args) {
		if (args.length == 0) {
			System.out.println("usage: java ... <arg1> <arg2> ...");
			System.exit(0);
		}

		JFrame frame = new JFrame();
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		Container container = frame.getContentPane();

		frame.pack();

		Dimension screen = 
			Toolkit.getDefaultToolkit().getScreenSize();
		int x =	(screen.width - frame.getWidth()) / 2;
		int y = (screen.height - frame.getHeight()) / 2;

		frame.setLocation(x, y);

		frame.setVisible(true);
	}
}

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NIO API Reference Overview
This page lists New IO class packages and describes changes made to existing IO
classes in order to support New IO features.

New packages, classes, and interfaces:
java.niopackage: Buffers, which are used throughout the NIO APIs.
java.nio.channels package: Channels and selectors.

Note: The new InetSocketAddress and SocketAddress classes, while not strictly part of the NIO APIs, are used by them.

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慢

试试能不能格式化代码

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.io.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.border.*;

public class Test {
public static void main(String[] args) {
if (args.length == 0) {
System.out.println("usage: java ... <arg1> <arg2> ...");
System.exit(0);
}

JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container container = frame.getContentPane();

frame.pack();

Dimension screen = 
Toolkit.getDefaultToolkit().getScreenSize();
int x =	(screen.width - frame.getWidth()) / 2;
int y = (screen.height - frame.getHeight()) / 2;

frame.setLocation(x, y);

frame.setVisible(true);
}
}

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还行，不错。