Java compact3 javax.security.sasl Class SaslException（JDK8）

This implementation returns the cause that was supplied via one of the constructors requiring a Throwable, or that was set after creation with the Throwable.initCause(Throwable) method. While it is typically unnecessary to override this method, a subclass can override it to return a cause set by some other means. This is appropriate for a "legacy chained throwable" that predates the addition of chained exceptions to Throwable. Note that it is not necessary to override any of the PrintStackTrace methods, all of which invoke the getCause method to determine the cause of a throwable.

This method can be called at most once. It is generally called from within the constructor, or immediately after creating the throwable. If this throwable was created with Throwable.Throwable(Throwable) or Throwable.Throwable(String,Throwable), this method cannot be called even once.

An example of using this method on a legacy throwable type without other support for setting the cause is:

 try {
     lowLevelOp();
 } catch (LowLevelException le) {
     throw (HighLevelException)
           new HighLevelException().initCause(le); // Legacy constructor
 }