lasciando un attimo perdere le migliorie (che senno stiamo qua fino a domani probabilmente).
ho provato a modificare così:
codice:
public class Movimenti {

    private int entrate;
    private int uscite;
    private String causale;
    private String data;

    public Movimenti(int entrate, int uscite, String causale, String data) {
        this.entrate = entrate;
        this.uscite = uscite;
        this.causale = causale;
        this.data = data;
    }
....
    public boolean salva() {
        try {
            Connection conn = DriverManager.getConnection("jdbc:mysql://62.94.208.157:3306/banca?user=root&password=qwyjkzx");
            Statement stmt = conn.createStatement();
            int g = stmt.executeUpdate("insert into movimenti (entrate,uscite,causale,data) values(" + this.entrate + "," + this.uscite + ",'" + this.causale + "','" + this.data + "')");
            stmt.close();
            return true;
        } catch (Exception e) {
            JOptionPane.showMessageDialog(null, e.getMessage());
            return false;
        }
    }
in fase di esecuzione mi da questo errore:
codice:
Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: ""
        at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
        at java.lang.Integer.parseInt(Integer.java:470)
        at java.lang.Integer.parseInt(Integer.java:499)
        at banca.Banca.jButton1MouseClicked(Banca.java:182)
        at banca.Banca.access$100(Banca.java:17)
        at banca.Banca$2.mouseClicked(Banca.java:73)
        at java.awt.AWTEventMulticaster.mouseClicked(AWTEventMulticaster.java:253)
        at java.awt.Component.processMouseEvent(Component.java:6266)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
        at java.awt.Component.processEvent(Component.java:6028)
        at java.awt.Container.processEvent(Container.java:2041)
        at java.awt.Component.dispatchEventImpl(Component.java:4630)
        at java.awt.Container.dispatchEventImpl(Container.java:2099)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4574)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4247)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
        at java.awt.Container.dispatchEventImpl(Container.java:2085)
        at java.awt.Window.dispatchEventImpl(Window.java:2478)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)