Main.java

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

public class Main {
    public static void main(String[] args) {
        new Main().run();
    }

    private void run() {
        JFrame frame = new JFrame("Swing Test");
        JPanel rootBorderLayoutPanel = new JPanel(new BorderLayout());
        JPanel centerPanel = new JPanel();
        final JButton button1 = new JButton("ボタン1");
        button1.setOpaque(true);            //trueにするとコンポーネントの境界まで全部描画する。デフォルトはfalse
        button1.setBorderPainted(false);    //falseにすると枠線を描画しなくなる。デフォルトはtrue
        button1.setBackground(new Color(52, 152, 219));
        button1.setForeground(new Color(236, 240, 241));
        button1.setFont(new Font("", Font.BOLD, 13));
        button1.addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                button1.setForeground(button1.getForeground().darker());
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                button1.setForeground(button1.getForeground().brighter());
            }

            @Override
            public void mouseEntered(MouseEvent e) {
                button1.setBackground(button1.getBackground().darker());
            }

            @Override
            public void mouseExited(MouseEvent e) {
                button1.setBackground(button1.getBackground().brighter());
            }
        });
        centerPanel.add(button1);

        centerPanel.add(new JButton("ボタン2"));

        rootBorderLayoutPanel.add(centerPanel, BorderLayout.CENTER);
        frame.add(rootBorderLayoutPanel);
        frame.pack();
        frame.setVisible(true);
    }
}