What is String.repeat in Java?

Java 11 adds a new method called repeat to the String class. The repeat method returns a new string whose value is the concatenation of this string repeated n times, where n is passed as an argument.

Method signature

public String repeat​(int n)

// n -- The number of times the string needs to be repeated

Example

public class Main 
{
    public static void main(String[] args) {
        String str = ". ";
        System.out.println( str.repeat(5) ); //. . . . .
    }
}
// the above method will return a new string with ". " repeated five times
//. . . . .

The above code can be tested online here.

Points to note

  • If n = 0, then an empty string is returned.

  • If n = 1, then a reference to the original string is returned.

  • If n < 0, then IllegalArgumentException is thrown.

  • If the string is empty, then the repeat method will return an empty string for all positive n values.

  • If the resulting string is too big, then OutOfMemoryError exception will be thrown.

All the above cases are covered in the example below.

public class HelloWorld {
    public static void main(String[] args) {
      String str = "test";
      System.out.println("Passing n = 0 will return an empty string" + str.repeat(0));
      
      String oneTimeRepeatedString = str.repeat(1);
      System.out.println("Passing n = 1 will return a reference to this string " + oneTimeRepeatedString);
      System.out.println("Checking if references are equal by str == oneTimeRepeatedString " + (oneTimeRepeatedString == str) );
      
      try {
        System.out.println("Passing n < 0 will throw an IllegalArgumentException" + str.repeat(-1));
      } catch(Exception e) {
        System.out.println(e);
      }
    
      try {
        System.out.println("Passing larger n values will throw an OutOfMemoryError" +  str.repeat(Integer.MAX_VALUE));
      } catch(Exception e) {
        System.out.println(e);
      }
      
    }
}

You can execute the above code online here.

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