java - 按金额删除购物车中的产品

Question

我有一个注册应用程序，我必须在购物篮中添加删除选项。

现在我将按钮设置为循环，以便为每个产品创建一个按钮。这一切都很好，但每当我将多个相同的元素放入购物篮时，它也会将其删除，而不是减少数量。基本上我希望它像: cars aantal: 3 ，当我单击该产品的删除按钮时，aantal 是 2 直到其为 1，然后删除该项目。我知道这是通过设置标签文本来完成的，但标签数量与产品数量相关联。这是我的代码:

付款类别:

for (int i = 0; i < products.size(); i++) {
            Product product = products.get(i);
            productdelete = product;

lblamount = new JLabel(String.valueOf(WinkelApplication.getBasket().getProductAmount(productdelete)));
            lblamount.setBounds(410, verticalPosition + i * productOffset, 70, 20);
            lblamount.setFont(WinkelApplication.FONT_10_PLAIN);
            add(lblamount);

DeleteProduct deleteproduct = new DeleteProduct();

            JButton btnDeleteproduct = new JButton("X");
            btnDeleteproduct.setBounds(380, verticalPosition + i * productOffset, 20, 20);
            btnDeleteproduct.setFont(WinkelApplication.FONT_10_BOLD);
            btnDeleteproduct.setName("" + i);
            btnDeleteproduct.addActionListener(deleteproduct);
            add(btnDeleteproduct);
}

删除产品类别:

public void productlist(){
    List<Product> products = WinkelApplication.getBasket().getProducts();

    for(int i = 0; i < products.size(); i++){
        deleteproduct = products.get(i);
    }
    }

    public void actionPerformed(ActionEvent event){
        productlist();

        productamount = WinkelApplication.getBasket().getProductAmount(deleteproduct);

        if(productamount == 1){
            WinkelApplication.getBasket().deleteProduct(deleteproduct);
        }else if (productamount > 1){
            productamount--;
            WinkelApplication.getBasket().setProductAmount(productamount);
            WinkelApplication.getInstance().showPanel(new view.Payment());
        }

    }

每当我将此代码放在其他地方加载时:

productamount = WinkelApplication.getBasket().getProductAmount(deleteproduct);

它给了我一个错误:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at model.Basket.getProductAmount(Basket.java:62)
    at view.DeleteProduct.productlist(DeleteProduct.java:27)
    at view.DeleteProduct.actionPerformed(DeleteProduct.java:34)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
    at java.awt.Component.processMouseEvent(Component.java:6382)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3275)
    at java.awt.Component.processEvent(Component.java:6147)
    at java.awt.Container.processEvent(Container.java:2083)
    at java.awt.Component.dispatchEventImpl(Component.java:4744)
    at java.awt.Container.dispatchEventImpl(Container.java:2141)
    at java.awt.Component.dispatchEvent(Component.java:4572)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4619)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4280)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4210)
    at java.awt.Container.dispatchEventImpl(Container.java:2127)
    at java.awt.Window.dispatchEventImpl(Window.java:2489)
    at java.awt.Component.dispatchEvent(Component.java:4572)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:704)
    at java.awt.EventQueue.access$400(EventQueue.java:82)
    at java.awt.EventQueue$2.run(EventQueue.java:663)
    at java.awt.EventQueue$2.run(EventQueue.java:661)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
    at java.awt.EventQueue$3.run(EventQueue.java:677)
    at java.awt.EventQueue$3.run(EventQueue.java:675)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:674)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Answer 1

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

清楚地表明您尝试获取的对象为 null 尝试进行 null 检查 if(WinkelApplication.getBasket()!=null)