Apple WebObjects 3.5 Manuel d'utilisateur télécharger pdf (Page 61)

Programming Pitfalls to Avoid

•WebScript supports only objects that inherit from NSObject. As most

objects inherit from NSObject, this limitation is easy to overlook.

Notably, EOFault does not inherit from NSObject, so you cannot use it

in WebScript code.

• The == operator is supported only for NSNumber objects. If you use

== to compare two objects of any other class, the operator compares the

addresses of the two objects, not the values of the two objects. To test

the equality of two objects, use the

isEqual: method.

NSString *string1, *string2;

// WRONG!

if (aString1 == aString2) ...

// Right

if ([aString1 isEqual:string2]) ...

• The postincrement and postdecrement operators are not supported. If

you use them, you won’t receive an error message. Instead, they behave

like preincrement and predecrement operators.

i = 0;

if (i++ < 1 )

// This code never gets executed.

•WebScript always evaluates both sides of a Boolean expression (such as

&& and ||). You should make sure that the second half of an expression

does not produce an error.

// WRONG! produces a divide by 0 if a is 0.

if ((a == 0) || (b / a) > 5) ...

For more information, see the chapter “The WebScript Language” (page

163).

Java Programming Pitfalls

When debugging Java code, watch out for the following tricky spots:

•You can’t deﬁne multiple constructors or overloaded methods for the

classes WebApplication, WebSession, Component, or any other class

that originates as an Objective-C class. For example, the following code

causes your application to crash:

public class MyComponent extends Component {

public void myMethod() { .... }

//WRONG! Overloaded method causes runtime error.

public void myMethod(int anInt) { ... }

}

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Apple WebObjects 3.5 Manuel d'utilisateur Page 61