局部变量范围问题 怎么解决呢？

确实存在范围问题，因为statement这里定义了一个本地方法变量：

protected void createContents  {
    ...
    Statement statement = null; // local variable
    ...
     btnInsert.addMouseListener(new MouseAdapter  { // anonymous inner class
        @Override
        public void mouseDown(MouseEvent e) {
            ...
            try {
                statement.executeUpdate(query); // local variable out of scope here
            } catch (sqlException e1) {
                e1.printstacktrace ;
            }
            ...
    });
}

当您尝试在mouseDown 方法内部访问此变量时，您尝试从匿名内部类内部访问局部变量，并且作用域不够。因此，它肯定是final（不可能给出您的代码）或声明为类成员，以便内部类可以访问此statement变量。

使statement一个类成员而不是一个局部变量：

public class A1 { // Note Java Code Convention, also class name should be meaningful   
    private Statement statement;
    ...
}

定义另一个最终变量，并使用该变量，如@HotLicks建议：

protected void createContents  {
    ...
    Statement statement = null;
    try {
        statement = connect.createStatement ;
        final Statement innerStatement = statement;
    } catch (sqlException e) {
        // Todo Auto-generated catch block
        e.printstacktrace ;
    }
    ...
}

重新考虑您的方法。如果在按下按钮statement之前不使用变量，btnInsert那么 在 实际发生 之前 创建连接是没有意义的。您可以这样使用所有局部变量：

btnInsert.addMouseListener(new MouseAdapter  {
   @Override
   public void mouseDown(MouseEvent e) {
       try {
           Class.forName("com.MysqL.jdbc.Driver");
           try (Connection connect = DriverManager.getConnection(...);
                Statement statement = connect.createStatement ) {

                // execute the statement here

           } catch (sqlException ex) {
               ex.printstacktrace ;
           }

       } catch (ClassNotFoundException ex) {
           e.printstacktrace ;
       }
});

尝试statemet.executeUpdate 在我的代码中执行时出现以下错误：

Local variable statement defined in an enclosing scope must be final or effectively final.

到目前为止，这是我的代码：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;.

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.MouseAdapter;
import org.eclipse.swt.events.MouseEvent;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Label;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Text;

public class a1 {

    protected Shell shell;
    private Text text;
    private Text text_1;
    private Text text_2;
    private Text text_3;

    /**
     * Launch the application.
     * @param args
     */
    public static void main(String[] args) {
        try {
            a1 window = new a1 ;
            window.open ;
        } catch (Exception e) {
            e.printStackTrace ;
        }
    }

    /**
     * Open the window.
     */
    public void open  {
        Display display = Display.getDefault ;
        createContents ;
        shell.open ;
        shell.layout ;
        while (!shell.isDisposed ) {
            if (!display.readAndDispatch ) {
                display.sleep ;
            }
        }
    }

    /**
     * Create contents of the window.
     */
    protected void createContents  {

        Connection connect = null;

        ResultSet resultSet = null;

        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace ;
        }
        try {
            connect = DriverManager.getConnection("jdbc:mysql://localhost/railwaydb","root","");
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace ;
        }

        Statement statement = null;
        // statements allow to issue SQL queries to the database
        try {
            statement = connect.createStatement ;
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace ;
        }

        shell = new Shell ;
        shell.setSize(450,300);
        shell.setText("SWT Application");

        Label lblName = new Label(shell,SWT.NONE);
        lblName.setBounds(10,43,47,15);
        lblName.setText("Name");

        Label lblFrom = new Label(shell,SWT.NONE);
        lblFrom.setBounds(10,74,55,15);
        lblFrom.setText("From");

        Label lblTo = new Label(shell,SWT.NONE);
        lblTo.setBounds(10,105,15);
        lblTo.setText("To");

        Label lblPrice = new Label(shell,SWT.NONE);
        lblPrice.setBounds(10,137,15);
        lblPrice.setText("Price");

        text = new Text(shell,SWT.BORDER);
        text.setBounds(64,76,21);

        text_1 = new Text(shell,SWT.BORDER);
        text_1.setBounds(64,21);

        text_2 = new Text(shell,SWT.BORDER);
        text_2.setBounds(64,21);

        text_3 = new Text(shell,SWT.BORDER);
        text_3.setBounds(64,21);

        Label lblRailwayDatabase = new Label(shell,SWT.NONE);
        lblRailwayDatabase.setBounds(174,10,97,15);
        lblRailwayDatabase.setText("Railway Database");

        Label lblCreateView = new Label(shell,SWT.NONE);
        lblCreateView.setBounds(189,15);
        lblCreateView.setText("Create View");

        Button btnName = new Button(shell,SWT.CHECK);
        btnName.setBounds(189,73,93,16);
        btnName.setText("Name");

        Button btnFrom = new Button(shell,SWT.CHECK);
        btnFrom.setBounds(189,16);
        btnFrom.setText("From");

        Button btnTo = new Button(shell,SWT.CHECK);
        btnTo.setBounds(189,16);
        btnTo.setText("To");

        Button btnPrice = new Button(shell,SWT.CHECK);
        btnPrice.setBounds(189,171,16);
        btnPrice.setText("Price");

        Button btnInsert = new Button(shell,SWT.NONE);
        btnInsert.addMouseListener(new MouseAdapter  {
            @Override
            public void mouseDown(MouseEvent e) {
                String name = text.getText ;
                String from = text_1.getText ;
                String to = text_2.getText ;
                String price = text_3.getText ;

                String query = "INSERT INTO booking (name,fromst,tost,price) VALUES ('"+name+"','"+from+"','"+to+"','"+price+"')";
                try {
                    statement.executeUpdate(query);
                } catch (SQLException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace ;
                }
            }
        });
        btnInsert.setBounds(10,75,25);
        btnInsert.setText("Insert");

        Button btnView = new Button(shell,SWT.NONE);
        btnView.setBounds(307,25);
        btnView.setText("View");

        Button btnIndex = new Button(shell,SWT.NONE);
        btnIndex.setBounds(307,127,25);
        btnIndex.setText("Index");

    }
}

我也尝试设置statementfinal，但声明给了我另一个错误。

标签： #shell #addMouseListener #变量