Month: September 2015

java.util.IllegalFormatConversionException when using System.out.format()

A few weeks ago I described how to format output using System.out.printl() and System.out.println() methods…

Try to run the code below:

double avgAge = 245 / 34;  
System.out.format("Average age is %d.", avgAge);

Without doubts you’ll get an exception thrown at runtime:

Average age is Exception in thread "main" 
java.util.IllegalFormatConversionException: 
d != java.lang.Double
    at java.util.Formatter$FormatSpecifier.failConversion(Unknown Source)
    at java.util.Formatter$FormatSpecifier.printInteger(Unknown Source)
    at java.util.Formatter$FormatSpecifier.print(Unknown 

Collections – sorting and searching

In order to sort a Collection, one should use java.util.Collections class as follows (assuming ArrayList will be used):

List another object

• the drawback: there’s only one way of sorting

Example of the class implementing Comparable interface:

class Book implements Comparable {
    private String title;
    
    public String getTitle() {
        return title;
    }

    public void setTitle(String title_p) {
        title = title_p;