question: @ Override public String toString ( ) { StringBuilder result = new StringBuilder ( "EQUATIONS:\n" ) ; Enumeration < GraphNode > v = equations . enumerateNodes ( ) ; for ( int i = 0 ; i < equations . numberOfNodes ( ) ; i ++ ) { result . append ( i ) ; result . append ( " : " ) ; result . append ( v . nextElement ( ) ) ; result . append ( '\n' ) ; } return result . toString ( ) ; }
target:  Return a string representation of the system