System.out.printf 和 String.format 的区别

Question

May I know what is the difference between the two in java? I am reading a book and it uses both methods to display strings.

Answer 1

The first one writes to the stdout and the second one returns a String object.

Which to use depends on the sole purpose. If you want to display the string in the stdout (console), then use the first. If you want to get a handle to the formatted string to use further in the code, then use the second.

Answer 2

String.format returns a new String, while System.out.printf just displays the newly formatted String to System.out, sometimes known as the console.

These two snippets of code are functionally equivalent:

String formattedString = String.format("%d is my favorite number", 42);
System.out.print(formattedString);

and

System.out.printf("%d is my favorite number", 42);

Answer 3

String.format formats strings, doesn't display them. I think you mean System.out.println(String.format("......", ....)) or some similar construct ?

Answer 4

String.format returns a formatted string. System.out.printf also prints the formatted string.

Answer 5

These two methods exhibit the exact same behavior. We can use the format(...) with String, Java.util.Formatter (J2SE 5) and also with PrintWriter.

Answer 6

The key different between System.out.printf() and String.format() methods is that

• printf() prints the formatted String into console much like System.out.println() but
• format() method return a formatted String, which you can store or use the way you want.

Otherwise nature of use is different according to their functionalities -

A sample example to add leading zeros into a numbers :

int num = 5;      
String str = String.format("%03d", num);  // 0005    
System.out.printf("Original number %d, leading with zero : %s", num, str);