Java String substring() with examples

This method returns a string which is a subset/portion of another string.

There are two variations of this method.

public String substring(int beginIndex)

and

public String substring(int beginIndex, int endIndex)

public String substring(int beginIndex)

This method returns a string from beginIndex to the end of the string.

NB:The index starts at 0.

e.g.

String str = "whitepiano";

System.out.println(str.substring(3));

The above code outputs 

tepiano

If the beginIndex is larger than the String size or less than 0(negative),then java.lang.StringIndexOutOfBoundsException will be thrown.

Calling the above code with beginIndex as 0 returns the entire string i.e

String str = "whitepiano";

System.out.println(str.subSstring(0));

 Outputs 

whitepiano

public String substring(int beginIndex,  int endIndex)

This method returns a string formed from beginIndex(inclusive) to endIndex-1(endIndex is exclusive)

It will throw java.lang.StringIndexOutOfBoundsException if beginIndex is negative,endIndex is greater than string length or beginIndex is larger than endIndex.

e.g

String str = "whitepiano";

System.out.println(str.substring(2,6));

The above code will output  itep

Some common use cases of String substring method.

1.Suffix and Prefix extraction e.g getting the currency of amount to process from a string containing both currency code and amount e.g USD300.21 -> "USD300.21".substring(3) will return the amount 300.21.This is assuming that currency code will always be 3 characters long.