visual basic barcode printing What a Method-Local Inner Object Can and Can t Do in Java

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What a Method-Local Inner Object Can and Can t Do
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A method-local inner class can be instantiated only within the method where the inner class is defined. In other words, no other code running in any other method inside or outside the outer class can ever instantiate the method-local inner class. Like regular inner class objects, the method-local inner class object shares a special relationship with the enclosing (outer) class object, and can access its private (or any other) members. However, the inner class object cannot use the local variables of the method the inner class is in. Why not Think about it. The local variables of the method live on the stack, and exist only for the lifetime of the method. You already know that the scope of a local variable is limited to the method the variable is declared in. When the method ends, the stack
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8: Inner Classes
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frame is blown away and the variable is history. But even after the method completes, the inner class object created within it might still be alive on the heap if, for example, a reference to it was passed into some other code and then stored in an instance variable. Because the local variables aren t guaranteed to be alive as long as the method-local inner class object, the inner class object can t use them. Unless the local variables are marked final! The following code attempts to access a local variable from within a method-local inner class:
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class MyOuter2 { private String x = "Outer2"; void doStuff() { String z = "local variable"; class MyInner { public void seeOuter() { System.out.println("Outer x is " + x); System.out.println("Local variable z is " + z); } // close inner class method } // close inner class definition } // close outer class method doStuff() } // close outer class
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Compiling the preceding code really upsets the compiler:
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MyOuter2.java:8: local variable z is accessed from within inner class; needs to be declared final System.out.println("Local variable z is " + z); ^
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Marking the local variable z as final fixes the problem:
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final String z = "local variable"; // Now inner object can use it
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And just a reminder about modifiers within a method: the same rules apply to method-local inner classes as to local variable declarations. You can t, for example, mark a method-local inner class public, private, protected, static, transient, and the like. The only modifiers you can apply to a method-local inner class are abstract and final. (But of course, never both of those at the same time as with any other class or method.)
Anonymous Inner Classes
CERTIFICATION OBJECTIVE
Anonymous Inner Classes
So far we ve looked at defining a class within an enclosing class (a regular inner class), and within a method (a method-local inner class). Finally, we re going to look at the most unusual syntax you might ever see in Java, inner classes declared without any class name at all (hence the word anonymous). And if that s not weird enough, you can even define these classes not just within a method, but within an argument to a method. We ll look first at the plain old (as if there is such a thing as a plain old anonymous inner class) version (actually, even the plain old version comes in two flavors), and then at the argument-declared anonymous inner class. Perhaps your most important job here is to learn to not be thrown when you see the syntax. The exam is littered with anonymous inner class code; you might see it on questions about threads, wrappers, overriding, garbage collection, and you get the idea.
Plain Old Anonymous Inner Classes, Flavor One
Check out the following legal-but-strange-the-first-time-you-see-it code:
class Popcorn { public void pop() { System.out.println("popcorn"); } } class Food { Popcorn p = new Popcorn() { public void pop() { System.out.println("anonymous popcorn"); } }; }
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