8.5 TextPicture

The TextPicture class allows strings to be inserted into a pictorial template. This class separates the specification of the position and width of a field from the formatting of text within the field. TextPicture objects allow you to place fields in text in a visually intuitive manner.

In its simplest form, the TextPicture class can be used like the C language printf() function. In keeping with Java's String-centered I/O, TextPicture allows you to substitute values into a line of text:

public void trivial(String string, int number)
 {
   TextPicture picture = new TextPicture("A _ is worth _ words.");
   System.out.println(picture.arg(string).arg(number));
 }

An alternative way to write the same thing is:

public void trivial(String string, int number)
 {
   TextPicture picture = new TextPicture
     ("A _ is worth _words.").arg(string).arg(number);
   picture.println(System.out);
 }

For this simple example there is no clear advantage over Java's String concatenation:

public void trivial(String string, int number)
{
 System.out.println("A " + string + " is worth " + number + "words.");
}

For more complicated formatting, however, String concatenation can become difficult to read. In complex cases, a separation of the constant from the variable improves readability. Compare this code:

   
TextPicture fmt =
  new TextPicture("<tr><td> _ </td><td> _ </td><td> _ </td></tr>");
for(int i = 0; i < rows; i++)
  fmt.arg(col1[i]).arg(col2[i]).arg(col3[i]).println(System.out);

With this code:

for(int i = 0; i < rows; i++)
  System.out.println("<tr><td> " + col1 + " </td><td> " +
    col2 + " </td><td> " + col3 + " </td></tr>");

In addition, TextPicture allows you to specify field widths pictorially.

String hline =   "----------------------------------";
String headers = "| Credits  |  Debits  | Balance  |";
String row =     "| ________ | ________ | ________ |"
TextPicture fmt = new TextPicture(row);
System.out.println(hline);  
System.out.println(headers);  
for(int i = 0; i < rows; i++)
  fmt.arg(credits[i]).arg(debits[i]).arg(balances[i]).println(System.out);
System.out.println(hline);

This would produce a text table like this:

----------------------------------
| Credits  |  Debits  | Balance  |
----------------------------------
|       50 |          |       50 |
|          |     4.95 |    45.05 |
|          |    29.99 |    15.06 |
|          |      8.5 |     6.56 |
|       50 |          |    56.56 |
|          |     37.5 |    19.06 |
----------------------------------