Throwable initCause() method in Java with Examples

Last Updated : 19 Aug, 2019

The initCause() method of Throwable class is used to initialize the cause of the this Throwable with the specified cause passed as a parameter to initCause(). Actually, the cause is the throwable that caused this throwable Object to get thrown when an exception occurs. This method can be called only once. Generally, This method is called from within the constructor, or immediately after creating the throwable. If the calling Throwable is created by using Throwable(Throwable) or Throwable(String, Throwable), then this method cannot be called even once.

Syntax:

public Throwable initCause?(Throwable cause)

Parameters: This method accepts cause as a parameter which represents the cause of the this Throwable.

Returns: This method returns a reference to this Throwable instance.

Exception: This method throws:

IllegalArgumentException if cause is this throwable.
IllegalStateException if this throwable was created with Throwable(Throwable) or Throwable(String, Throwable), or this method has already been called on this throwable.

Below programs illustrate the initCause method of Throwable class:

Example 1:

// Java program to demonstrate 
// the initCause() Method. 
  
import java.io.*; 
  
class GFG { 
  
    // Main Method 
    public static void main(String[] args) 
        throws Exception 
    { 
  
        try { 
  
            testException1(); 
        } 
  
        catch (Throwable e) { 
  
            System.out.println("Cause : "
                               + e.getCause()); 
        } 
    } 
  
    // method which throws Exception 
    public static void testException1() 
        throws Exception 
    { 
  
        // ArrayIndexOutOfBoundsException Exception 
        // This exception will be used as a Cause 
        // of another exception 
        ArrayIndexOutOfBoundsException 
            ae 
            = new ArrayIndexOutOfBoundsException(); 
  
        // create a new Exception 
        Exception ioe = new Exception(); 
  
        // initialize the cause and throw Exception 
        ioe.initCause(ae); 
  
        throw ioe; 
    } 
} 

Output:

Cause : java.lang.ArrayIndexOutOfBoundsException

Example 2:

// Java program to demonstrate 
// the initCause() Method. 
  
import java.io.*; 
  
class GFG { 
  
    // Main Method 
    public static void main(String[] args) 
        throws Exception 
    { 
  
        try { 
  
            // add the numbers 
            addPositiveNumbers(2, -1); 
        } 
        catch (Throwable e) { 
  
            System.out.println("Cause : "
                               + e.getCause()); 
        } 
    } 
  
    // method which adds two positive number 
    public static void addPositiveNumbers(int a, int b) 
        throws Exception 
    { 
  
        // if Numbers are Positive 
        // than add or throw Exception 
        if (a < 0 || b < 0) { 
  
            // create a Exception 
            // when Numbers are not Positive 
            // This exception will be used as a Cause 
            // of another exception 
            Exception 
                ee 
                = new Exception("Numbers are not Positive"); 
  
            // create a new Exception 
            Exception anotherEXe = new Exception(); 
  
            // initialize the cause and throw Exception 
            anotherEXe.initCause(ee); 
  
            throw anotherEXe; 
        } 
  
        else { 
  
            System.out.println(a + b); 
        } 
    } 
} 

Output:

Cause : java.lang.Exception: Numbers are not Positive

References: https://docs.oracle.com/javase/10/docs/api/java/lang/Throwable.html#initCause(java.lang.Throwable)

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