visual basic barcode program The preceding declarations will deliver you a nice compiler error message similar to in Java

Drawer PDF 417 in Java The preceding declarations will deliver you a nice compiler error message similar to

The preceding declarations will deliver you a nice compiler error message similar to
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MyClass.java:18: illegal combination of modifiers: abstract and synchronized abstract synchronized void foo(); ^ MyClass.java:19: illegal combination of modifiers: abstract and strictfp abstract strictfp void foof(); ^ MyClass.java:20: illegal combination of modifiers: abstract and native abstract native void poof(); ^
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Finally, you need to know that the abstract modifier can never be combined with the static modifier. We ll cover static methods later in this objective, but for now just remember that the following would be illegal:
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abstract static void doStuff();
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And it would give you an error that should be familiar by now:
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MyClass.java:2: illegal combination of modifiers: abstract and static abstract static void doStuff(); ^
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Synchronized Methods The synchronized keyword indicates that a method can be accessed by only one thread at a time. We ll discuss this nearly to death in 9, but for now all we re concerned with is knowing that the synchronized modifier can be applied only to methods not variables, not classes, just methods. A typical synchronized declaration looks like this:
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public synchronized Record retrieveUserInfo(int id) { }
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You should also know that the synchronized modifier can be matched with any of the four access control levels (which means it can be paired with any of the three access modifier keywords). And you can also combine synchronized with final, but never with abstract. Synchronization is an implementation issue; only the programmer can decide whether a method needs to be marked as synchronized. If you declare a method like the following,
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abstract synchronized void doStuff();
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2: Declarations and Access Control
you ll get a compiler error similar to this:
MyClass.java:2: illegal combination of modifiers: abstract and synchronized abstract synchronized void doStuff(); ^
Native Methods The native modifier indicates that a method is implemented in a platform-dependent language, such as C. You don t need to know how to use native methods for the exam, other than knowing that native is a modifier (thus a reserved keyword), native can never be combined with abstract, and native can be applied only to methods not classes, not variables, just methods. Strictfp Methods We looked earlier at using strictfp as a class modifier, but even if you don t declare a class as strictfp, you can still declare an individual method as strictfp. Remember, strictfp forces floating points (and any floating-point operations) to adhere to the IEE754 standard. With strictfp, you can predict how your floating points will behave regardless of the underlying platform the JVM is running on. The downside is that if the underlying platform is capable of supporting greater precision, a strictfp method won t be able to take advantage of it. You ll need to have the IEEE754 standard pretty much memorized that is, if you need something to help you fall asleep. For the exam, however, you don t need to know anything about strictfp other than what it s used for, that it can modify a class or nonabstract method declaration, and that a variable can never be declared strictfp.
Variable Declarations
We ve already discussed variable access, which refers to the ability of code in one class to access a variable in another class. In this section we ll look at the other keywords that apply to variable declarations, but first we ll do a quick review of the difference between instance and local variables. Instance Variables Instance variables are defined inside the class, but outside of any method, and are only initialized when the class is instantiated. Instance variables are the fields that belong to each unique object. For example, the following code defines fields (instance variables) for the name, title, and manager for employee objects:
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class Employee { // define fields (instance variables) for employee instances private String name; private String title, private String manager; // other code goes here including access methods for private fields }
The preceding Employee class says that each employee instance will know its own name, title, and manager. In other words, each instance can have its own unique values for those three fields. If you see the term field, instance variable, property, or attribute, they mean virtually the same thing. (There actually are subtle but occasionally important distinctions between the terms, but those distinctions aren t used on the exam.) For the exam, you need to know that instance variables
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