How to Format Columns in Java

Your Java code can output columns of aligned field values.

Java code often needs to output tables with rows and columns. Programs generate a table by generating one row at a time. However, in order for the fields in each row to conform to a table format, instances of the same field in different rows must be aligned with each other and with the corresponding column headings. The built-in Java libraries support formatted output. You can write Java code that takes variable-length field values and formats it into neat columns.

Instructions

1. Include the following lines at the beginning of your Java code:

   import java.io.PrintStream;

   PrintStream myStream = new PrintStream();

   You can use any instance of the PrintStream class to receive the formatted output. In particular, the program's standard output -- System.out -- is an instance of PrintStream.

2. Format a column entry with an integer value by making it fit into the width of the column, as in the following sample code:

   int myInt = 46;

   myStream.format("%5d",myInt);

   Replace "5" with the width of the column. The example will send " 46" -- the integer value, right-justified by default, preceded by three spaces to occupy five places in total -- to "myStream".

3. Format a column entry with a floating-point value by making it fit into the width of the column, as in the following sample code:

   float myFloat = 87.494;

   myStream.format("%6.2f",myFloat);

   Replace "6" with the total width of the column -- including the decimal point -- and "2" with the number of decimal places to show. The decimal points will also be lined up over the whole column. The example will send " 87.49" -- the floating-point value, right-justified by default, preceded by a single space to occupy six places in total -- to "myStream".

Tips & Warnings

• Consult the format specifiers in the documentation for "Java: Class PrintStream" for other possible formats you can use for your columns.

References

• Oracle: Java: Formatting Numeric Print Output
• Oracle: Java: Class PrintStream