Overloading methods Overloading of methods is a compiler trick to allow you to use the same name to perform different actions depending on parameters. Thus imagine you were designing the interface for a system to run mock Java certification exams (who could this be?). An answer may come in as an integer, a boolean or a text string. You could create a version of the method for each parameter type and give it a matching name thusanswerboolean(boolean answer){ } answerint(int answer){ }answerString(String answer){ } This would work but it means that future users of your classes have to be aware of more method names than is strictly necessary. It would be more useful if you could use a single method name and the compiler would resolve what actual code to call according to the type and number of parameters in the call. This is the heart of overloading methods, part of what is known as polymorphism.There are no keywords to remember in order to overload methods, you just create multiple methods with the same name but different numbers and or types of parameters. The names of the parameters are not important but the number and types must be different. Thus the following is an example of an overloaded answer methodvoid answer(String answer){ } void answer(int answer){ } The following is not an example of overloading and will cause a compile time error indicating a duplicate method declaration.void answer(String answer){ }void answer(String title){ }The return type does not form part of the signature for the purpose of overloading. Thus changing one of the above to have an int return value will still result in a compile time error, but this time indicating that a method cannot be redefined with a different return type. Overloaded methods do not have any restrictions on what exceptions can be thrown. That is something to worry about with overriding. Overriding methods Overriding a method means that its entire functionality is being replaced. Overriding is something done in a child class to a method defined in a parent class. To override a method a new method is defined in the child class with exactly the same signature as the one in the parent class. This has the effect of shadowing the method in the parent class and the functionality is no longer directly accessible. Java provides an example of overriding in the case of the equals method that every class inherits from the granddady parent Object. The inherited version of equals simply compares where in memory the instance of the class references. This is often not what is wanted, particularly in the case of a String. For a string you would generally want to do a character by character comparison to see if the two strings are the same. To allow for this the version of equals that comes with String is an overriden version that performs this character by character comparison.
final : final keyword can be used for class, method and variables. A final class cannot be subclassed and it prevents other programmers from subclassing a secure class to invoke insecure methods. A final method can’t be overridden. A final variable can’t change from its initialized value. finalize() : finalize() method is used just before an object is destroyed and can be called just prior to garbage collection. finally : finally, a key word used in exception handling, creates a block of code that will be executed after a try/catch block has completed and before the code following the try/catch block. The finally block will execute whether or not an exception is thrown. For example, if a method opens a file upon exit, then you will not want the code that closes the file to be bypassed by the exception-handling mechanism. This finally keyword is designed to address this contingency.
final最终(定义常量), finally在try|catch|最后用的, finalize
面向对象 OO，面向过程OP
Overloading of methods is a compiler trick to allow you to use the same name to perform different actions depending on parameters. Thus imagine you were designing the interface for a system to run mock Java certification exams (who could this be?). An answer may come in as an integer, a boolean or a text string. You could create a version of the method for each parameter type and give it a matching name thusanswerboolean(boolean answer){
}
answerint(int answer){
}answerString(String answer){
}
This would work but it means that future users of your classes have to be aware of more method names than is strictly necessary. It would be more useful if you could use a single method name and the compiler would resolve what actual code to call according to the type and number of parameters in the call. This is the heart of overloading methods, part of what is known as polymorphism.There are no keywords to remember in order to overload methods, you just create multiple methods with the same name but different numbers and or types of parameters. The names of the parameters are not important but the number and types must be different. Thus the following is an example of an overloaded answer methodvoid answer(String answer){
}
void answer(int answer){
}
The following is not an example of overloading and will cause a compile time error indicating a duplicate method declaration.void answer(String answer){
}void answer(String title){
}The return type does not form part of the signature for the purpose of overloading. Thus changing one of the above to have an int return value will still result in a compile time error, but this time indicating that a method cannot be redefined with a different return type. Overloaded methods do not have any restrictions on what exceptions can be thrown. That is something to worry about with overriding.
Overriding methods
Overriding a method means that its entire functionality is being replaced. Overriding is something done in a child class to a method defined in a parent class. To override a method a new method is defined in the child class with exactly the same signature as the one in the parent class. This has the effect of shadowing the method in the parent class and the functionality is no longer directly accessible. Java provides an example of overriding in the case of the equals method that every class inherits from the granddady parent Object. The inherited version of equals simply compares where in memory the instance of the class references. This is often not what is wanted, particularly in the case of a String. For a string you would generally want to do a character by character comparison to see if the two strings are the same. To allow for this the version of equals that comes with String is an overriden version that performs this character by character comparison.
你看看这个英文网站吧,基础概念基本都有
尤其感谢 liufei8463(武汉小兵) !