练习题（一） 杭州华云纸业有限公司（3301910221）从境外采购废纸（法定计量单位为千克）一批，拟加工成白卡纸后最终销往国内市场，货物进境后，华云公司自行向口岸海关办理报关手续。

import javax.swing.JPanel;import javax.swing.JFrame;import javax.swing.JButton;import javax.swing.JTextField;import java.awt.FlowLayout;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.awt.event.WindowAdapter;import java.awt.event.WindowEvent;public class Test extends JFrame. implements ActionListener{ private static final long serialVersionUID = 1L; private JPanel jPanel; private JButton jButton1,jButton2,jButton3; private JTextField tf1; public Test(String title) { super(title); init(); } private void init() { jPanel=new JPanel(); jPanel.setLayout(new FlowLayout()); tf1=new JTextField(20); jButton1=new JButton("按钮1"); jButton2=new JButton("按钮2"); jButton3=new JButton("按钮3"); jButton1.addActionListener(this); jButton2.addActionListener(this); jButton3.addActionListener(this); jPanel.add(tf1); jPanel.add(jButton1); jPanel.add(jButton2); jPanel.add(jButton3); this.add(jPanel); this.setSize(300,100); this.setResizable(false); this.setVisible(true); this.addWindowListener(new WindowAdapter() { public void windowClosing(final WindowEvent e) { System.exit(0); } }); } public void actionPerformed(ActionEvent e) { if(e.getSource().equals(jButton1)){ tf1.setText("按钮1"); } if(e.getSource().equals(jButton2)){ tf1.setText("按钮2"); } if(e.getSource().equals(jButton3)){ tf1.setText("按钮3"); } } public static void main(String[] args){ new Test("文字变换"); }}