Statements before super()
in [Java Programming]
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From: Mike Schilling on 11 Feb 2010 11:33 Patricia Shanahan wrote: > Mike Schilling wrote: >> Suppose the call to "super()" needn't be the first line of a >> constructor. Discuss the effect and/or legality of the following >> code: class MyClass extends YourClass >> { >> public MyClass(int i) >> { >> if ( i > 0) >> { >> super(i); >> } >> } >> ... >> >> > > The most complete way of dealing with this would be to have two > concepts, "definitely constructed" and "definitely not constructed" > that would be calculated in a similar way to "definitely assigned". > > At the start of the body of the constructor "definitely constructed" > is false and "definitely not constructed" is true. > > Use of super and this to call another constructor is permitted if, and > only if, "definitely not constructed" is true. > > References that use "this", return and fall through to the end of the > constructor are permitted if, and only if, "definitely constructed" > is true. > Even if neither is true, completion through throw of an exception is > permitted. > > In the example case, at the end of the if statement "definitely > constructed" is false because of the i >= 0 case. "definitely not > constructed is false because of the i < 0 case. There can be no more > super or this calls, and the constructor must complete by throwing an > exception. > > Constructors that follow the current standard would transition to > "definitely constructed" true and "definitely not constructed" false > after the first statement of the constructor body. Good Lord, Patricia, I said "discuss", not "develop the complete theory of" :-)
From: Eric Sosman on 11 Feb 2010 13:57 On 2/11/2010 11:33 AM, Mike Schilling wrote: > Patricia Shanahan wrote: >> [... sensible stuff ...] > Good Lord, Patricia, I said "discuss", not "develop the complete theory of" > :-) She's a PhD. That's what PhD's do. Get over it. :-) -- Eric Sosman esosman(a)ieee-dot-org.invalid
From: Lew on 11 Feb 2010 14:38 Patricia Shanahan wrote: >>> [... sensible stuff ...] Mike Schilling wrote: >> Good Lord, Patricia, I said "discuss", not "develop the complete >> theory of" >> :-) Eric Sosman wrote: > She's a PhD. That's what PhD's do. Get over it. :-) And a genius. That's what geniuses do, too. (No smiley because it's the simple truth.) -- Lew
From: Tom Anderson on 11 Feb 2010 15:02 On Wed, 10 Feb 2010, Mike Schilling wrote: > Suppose the call to "super()" needn't be the first line of a constructor. > Discuss the effect and/or legality of the following code: > > class MyClass extends YourClass > { > public MyClass(int i) > { > if ( i > 0) > { > super(i); > } > } > ... A relaxing of the current rule which didn't ban that would be remiss indeed. tom -- As Emiliano Zapata supposedly said, "Better to die on your feet than live on your knees." And years after he died, Marlon Brando played him in a movie. So just think, if you unionize, Marlon Brando might play YOU in a movie. Even though he's dead. -- ChrisV82
From: markspace on 11 Feb 2010 15:15
Tom Anderson wrote: > On Wed, 10 Feb 2010, Mike Schilling wrote: > >> Suppose the call to "super()" needn't be the first line of a constructor. >> Discuss the effect and/or legality of the following code: >> >> class MyClass extends YourClass >> { >> public MyClass(int i) >> { >> if ( i > 0) >> { >> super(i); >> } >> } >> ... > > A relaxing of the current rule which didn't ban that would be remiss > indeed. True, but something like this should be acceptable, imo: class MyClass extends YourClass { public MyClass(int i) { if ( i > 0) { super(i); } else { super(); } } ... Because now the object is definitely constructed and also we've done something useful that the current JLS doesn't allow us to do. |