When to Use fillInStackTrace Method in Java

The fillInStackTrace() is an important method of Throwable class in Java. The stack trace can be useful to determine where exactly the exception is thrown. There may be some situations where we need to rethrow an exception and find out where it is rethrown, we can use the fillInStackTrace() method in such scenarios.

Syntax

public Throwable fillInStackTrace()

Example

public class FillInStackTraceTest {
   public static void method1() throws Exception {
      throw new Exception("This is thrown from method1()");
   }
   public static void method2() throws Throwable {
      try {
         method1();
      } catch(Exception e) {
         System.err.println("Inside method2():");
            e.printStackTrace();
            throw e.fillInStackTrace(); // calling fillInStackTrace() method
      }
   }
   public static void main(String[] args) throws Throwable {
      try {
         method2();
      } catch (Exception e) {
         System.err.println("Caught Inside Main method()");
         e.printStackTrace();
      }
   }
}

Output

Inside method2():
java.lang.Exception: This is thrown from method1()
	at FillInStackTraceTest.method1(FillInStackTraceTest.java:3)
	at FillInStackTraceTest.method2(FillInStackTraceTest.java:7)
	at FillInStackTraceTest.main(FillInStackTraceTest.java:16)
Caught Inside Main method()
java.lang.Exception: This is thrown from method1()
   at FillInStackTraceTest.method2(FillInStackTraceTest.java:11)
   at FillInStackTraceTest.main(FillInStackTraceTest.java:16)