Java 上一个按钮循环

Question

除了第一个和最后一个按钮之外，我还尝试创建上一个和下一个按钮。我已经设法让他们全部工作。但是，我似乎无法让上一个和下一个按钮循环遍历数组，而是在到达末尾时出现错误。我什至不知道从哪里开始，但非常感谢所有帮助!

    JButton firstButton = new JButton("First");
    buttonPanel.add(firstButton);
    firstButton.addActionListener(new ActionListener()
    {
        public void actionPerformed(ActionEvent e)
        {
            bookIndex = 0;
            prepareDisplay(inventoryBook[bookIndex], textArea);
        }
    });

    JButton previousButton = new JButton("Previous");
    buttonPanel.add(previousButton);
    previousButton.addActionListener(new ActionListener()
    {
        public void actionPerformed(ActionEvent e)
        {
            bookIndex = bookIndex - 1;
            prepareDisplay(inventoryBook[bookIndex], textArea);
        }
    });

    JButton nextButton = new JButton("Next");
    buttonPanel.add(nextButton);
    nextButton.addActionListener(new ActionListener()
    {
        public void actionPerformed(ActionEvent e)
        {
            bookIndex = bookIndex + 1;
            prepareDisplay(inventoryBook[bookIndex], textArea);
        }
    });

    JButton lastButton = new JButton("Last");
    buttonPanel.add(lastButton);
    lastButton.addActionListener(new ActionListener()
    {   
        public void actionPerformed(ActionEvent e)
        {
            bookIndex = (inventoryBook.length - 1);
            prepareDisplay(inventoryBook[bookIndex], textArea);
        }
    });

Answer 1

在 previousButton 和 nextButton 的 actionPerformed 中，您需要检查当前的 bookIndex 是什么。分别减少或增加。对于 previousButton，如果当前 bookIndex == 0，则将 bookIndex 设置为 inventoryBook.length-1 而不是递减。对于 nextButton，如果 bookIndex == inventoryBook.length-1，则将 bookIndex 设置为 0 而不是递增。因此对于 nextButton:

        JButton nextButton = new JButton("Next");
        buttonPanel.add(nextButton);
        nextButton.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                if(bookIndex == inventoryBook.length - 1) {
                    bookIndex = 0;
                } else {
                    bookIndex = bookIndex + 1;
                }

                prepareDisplay(inventoryBook[bookIndex], textArea);
            }
        });