java - 查找当前索引并打印数组中的下一条记录

Question

我有一个程序，有5个按钮。该按钮用于从数组中查找第一个、最后一个、下一个和上一个记录。 我已经完成了第一条和最后一条记录，但我对从数组中查找下一条和上一条记录感到困惑。

public void fn(String s2)
{
    try
    {
        BufferedReader br=new BufferedReader(new FileReader("Student.txt"));
        String s=br.readLine();
        Book[] b=Book.StringToObj(s);

        if(s2.equals("Read Data"))
        {
            l5.setText(String.valueOf(b[0].id));
            l6.setText(String.valueOf(b[0].title));
            l7.setText(String.valueOf(b[0].price));
            l8.setText(String.valueOf(b[0].auth));
        }

        if(s2.equals("<<"))
        {
            if(l5.getText().equals(String.valueOf(b[0].id))&&l6.getText().equals(String.valueOf(b[0].title))&&l7.getText().equals(String.valueOf(b[0].price))&&l8.getText().equals(String.valueOf(b[0].auth)))
            {
                JOptionPane.showMessageDialog(this,"You are already at First Record");
            }
            else
            {
                    l5.setText(String.valueOf(b[0].id));
                    l6.setText(String.valueOf(b[0].title));
                    l7.setText(String.valueOf(b[0].price));
                    l8.setText(String.valueOf(b[0].auth));
            }

        }

        if(s2.equals(">>"))
        {
            if(l5.getText().equals(String.valueOf(b[b.length-1].id))&&l6.getText().equals(String.valueOf(b[b.length-1].title))&&l7.getText().equals(String.valueOf(b[b.length-1].price))&&l8.getText().equals(String.valueOf(b[b.length-1].auth)))
            {
                JOptionPane.showMessageDialog(this,"You are already at Last Record");
            }
            else
            {
                l5.setText(String.valueOf(b[b.length-1].id));
                l6.setText(String.valueOf(b[b.length-1].title));
                l7.setText(String.valueOf(b[b.length-1].price));
                l8.setText(String.valueOf(b[b.length-1].auth));
            }
        }

        if(s2.equals("<"))
        {


            if(l5.getText().equals(String.valueOf(b[0].id))&&l6.getText().equals(String.valueOf(b[0].title))&&l7.getText().equals(String.valueOf(b[0].price))&&l8.getText().equals(String.valueOf(b[0].auth)))
            {
                JOptionPane.showMessageDialog(this,"This is a First Record, Previous Record is Not Available");
            }
            else
            {
            }

        }

        if(s2.equals(">"))
        {

        }

    }
    catch(Exception e)
    {
    }   
}

当我单击“>”按钮时，我想要数组中的下一条记录。 我必须做什么？

Answer 1

为什么不将当前页面存储在像 int 这样的变量中，然后对其进行操作？

类似这样的事情:

int page = 0;
Book[] books;

public void init() 
{
    BufferedReader br = new BufferedReader(new FileReader("Student.txt"));
    String s = br.readLine();
    books = Book.StringToObj(s);
}

public void show()
{
    l5.setText(String.valueOf(books[page].id));
    l6.setText(String.valueOf(books[page].title));
    l7.setText(String.valueOf(books[page].price));
    l8.setText(String.valueOf(books[page].auth));
}

public void fn(String s2)
{
    try
    {
        if(s2.equals("Read Data"))
        {
            show();
        }

        if(s2.equals("<<"))
        {
            if (page == 0)
            {
                JOptionPane.showMessageDialog(this,"You are already at First Record");
            }
            else
            {
                page = 0;
                show();
            }
        }

        if(s2.equals(">>"))
        {
            if (page == books.length - 1)
            {
                JOptionPane.showMessageDialog(this,"You are already at Last Record");
            }
            else
            {
                page = books.length-1;
                show();
            }
        }

        if(s2.equals("<"))
        {
            if (page == 0)
            {
                JOptionPane.showMessageDialog(this,"This is a First Record, Previous Record is Not Available");
            }
            else
            {
                page--;
                show();
            }
        }

        if(s2.equals(">"))
        {
            if (page == books.length - 1)
            {
                JOptionPane.showMessageDialog(this,"You are already at Last Record");
            }
            else
            {
                page++;
                show();
            }
        }
    }
    catch(Exception e)
    {
    }   
}

请注意，我也将 books 移至全局范围，因为每次都再次读取该文件是没有意义的。