[Java][Resolved] StringBuilder cannot find symbol subString(int)

Problem Hint :

Cannot find symbol
Symbol: method substring(int)
location: class java.lang.StringBuilder

Run Time error msg:

Exceptiom in thread "main" javaa.lang.RuntimeException: Uncompilable source code at testb.Main.main (Main.java:17) Java Result:1

Source code:

public class Main {
 public static void main(String[] args) {
  StringBuilder s1 = new StringBuilder("Java");
                String s2 = "Love";
                s1.append(s2);
                s1.substring(4);
 }
}

Data type of s1 is StringBuilder, problem I face is an Compatible problem, there is substring method in 1.5 and later version but in StringBuilder but not in 1.5.

So what you do in 1.5version below is not trying to use substring() method in StringBuilder, you can inital a String and assign content in StringBuilder to that String, and use substring() method in String(). Or you can upgrade your Java verios yo 1.5 or above.

Reference:
https://javatutorialhq.com/java/lang/stringbuilder-class-tutorial/substring-method-example/