为什么这段代码不会在Java中引发错误？

Question

String s = "Hola";
System.out.println(s.substring(4));

4 is out of bounds, yet no error is thrown.

Why is that?

Thanks in advance.

Answer 1

Think of the argument to String.substring() as the number of characters to skip . So skipping 4 characters in "Hola" yields the empty string.

"Hola".substring(0) => "Hola"
"Hola".substring(1) => "ola"
"Hola".substring(2) => "la"
"Hola".substring(3) => "a"
"Hola".substring(4) => ""

The lowest argument for which an exception will be thrown on a 4-character string is 5.

Answer 2

The index of Strings starts at 0 and not 1. For example, in string "Hola",

index 0 would be H

index 1 would be o

index 2 would be l

index 3 would be a

Notice that there is no index 4. This is why you are getting an error. instead, change it to

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