Errors and exceptions in Java E

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Harriet Hampton
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1 Errors and exceptions in Java E Object Throwable Error VirtualMachineError InternalError OutOfMemoryError StackOverflowError UnknownError Exception RuntimeException ArithmeticException ArrayStoreException ClassCastException IllegalArgumentException NumberFormatException IndexOutOfBoundsException NegativeArraySizeException NullPointerException Exceptions of the API user defined Exceptions Copyright c 2002 Robert F. Stärk, Computer Science Department, ETH Zürich, Switzerland 1

2 Checked exceptions and throws clauses Definition. A class E is called a checked exception class iff E h Throwable E h Error E h RuntimeException Syntax of throws clauses: meth(d 1 x 1,..., D n x n ) throws E 1,..., E n body Constraint: E i h Throwable Definition. A Method msig throws more specific exceptions in A than in B, iff for each class E occurring in the throws clause of msig in A there exists a class F in the throws clause of msig in B such that E h F. Constraint. If a method A/msig directly overrides B/msig, then msig throws more specific exceptions in A than in B. Copyright c 2002 Robert F. Stärk, Computer Science Department, ETH Zürich, Switzerland 2

3 Syntax of Java E Stm ::=... throw Exp; try Block catch (Class 1 Loc 1 ) Block 1... catch (Class n Loc n ) Block n Stm finally Block Definition. An exception E is allowed at a position α, iff one of the following conditions is true: E h Error E h RuntimeException The position α is in a try block and at least one catch clause of the try statement has a parameter of type F such that E h F The position α is in the body of a method or constructor declaration and there exists a class F in the throws clause of the declaration such that E h F Copyright c 2002 Robert F. Stärk, Computer Science Department, ETH Zürich, Switzerland 3

4 Type constraints for Java E catch (E loc) block E h Throwable. throw α exp; T (α) h Throwable and T (α) is allowed at position α. α (exp 0.C /msig(exps)) Each class E occurring in the throws clause of msig in C is allowed at position α. α C.msig(exps) Each class E occurring in the throws clause of msig in C is allowed at position α. Copyright c 2002 Robert F. Stärk, Computer Science Department, ETH Zürich, Switzerland 4

5 Vocabulary of the ASM for Java E Abr = Break(Lab) Continue(Lab) Return Return(Val) Exc(Ref) execjava E = execjavaexp E execjavastm E Transition rules for Java E failup(exc) = yieldup(throw new exc(); ) fail(exc) = yield(throw new exc(); ) Copyright c 2002 Robert F. Stärk, Computer Science Department, ETH Zürich, Switzerland 5

6 Transition rules for Java E (Expressions) execjavaexp E = case context(pos) of α val 1 bop val 2 if bop divmod iszero(val 2 ) then failup(arithmeticexception) ref.c/f if ref = null then failup(nullpointerexception) α ref.c/f = val if ref = null then failup(nullpointerexception) α ref.c/m (vals) if ref = null then failup(nullpointerexception) (c) ref if ref null classof (ref ) c then failup(classcastexception) Copyright c 2002 Robert F. Stärk, Computer Science Department, ETH Zürich, Switzerland 6

7 Transition rules for Java E (Statements) execjavastm E = case context(pos) of throw α exp; pos := α throw ref ; if ref = null then failup(nullpointerexception) else yieldup(exc(ref )) try α stm catch... pos := α try Norm catch... yieldup(norm) try Exc(ref ) catch (c 1 x 1 ) β 1stm 1... catch (c n x n ) β n stm n if 1 j n : classof (ref ) h c j then let j = min{i classof (ref ) h c i } pos := β j locals := locals {(x j, ref )} else yieldup(exc(ref )) try abr catch (c 1 x 1 ) β 1stm 1... catch (c n x n ) β n stm n yieldup(abr) try α Exc(ref )... catch (c i x i ) Norm... yieldup(norm) try α Exc(ref )... catch (c i x i ) abr... yieldup(abr) α stm 1 finally β stm 2 pos := α Norm finally β stm pos := β abr finally β stm pos := β α s finally Norm yieldup(s) α s finally abr yieldup(abr) Copyright c 2002 Robert F. Stärk, Computer Science Department, ETH Zürich, Switzerland 7

8 Transition rules for Java E (Statements continued) execjavastm E = case context(pos) of lab : Exc(ref ) yieldup(exc(ref )) static α Exc(ref ) if classof (ref ) h Error then yieldup(exc(ref )) else failup(exceptionininitializererror) Exc(ref ) if pos = firstpos null(frames) then exitmethod(exc(ref )) if methnm(meth) = "<clinit>" then classstate(classnm(meth)) := Unusable Copyright c 2002 Robert F. Stärk, Computer Science Department, ETH Zürich, Switzerland 8

9 Transition rules for Java E (continued) initialize(c) =... if classstate(c) = Unusable then fail(noclassdeffounderr) propagatesabr(phrase) = phrase lab : s phrase static s phrase try... phrase s 1 finally s 2 Copyright c 2002 Robert F. Stärk, Computer Science Department, ETH Zürich, Switzerland 9

Threads in Java T Syntax of Java T. Stm :=... synchronized (Exp) Stm. Native Methods for threads:

Threads in Java T Syntax of Java T Stm :=... synchronized (Exp) Stm Native Methods for threads: Thread/start() Thread/interrupt() Thread/interrupted() Thread/isInterrupted() Object/wait() Object/notify()