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Java final modifier

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问题 I was told that, I misunderstand effects of final . What are the effects of final keyword? Here is short overview of what I think, I know: Java final modifier (aka aggregation relation) primitive variables : can be set only once. (memory and performance gain) objects variables : may be modified, final applies to object reference. fields : can be set only once. methods : can\'t be overridden, hidden. classes : can\'t be extended. garbage collection : will force Java generational garbage

private final static attribute vs private final attribute

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问题 In Java, what\'s the difference between: private final static int NUMBER = 10; and private final int NUMBER = 10; Both are private and final , the difference is the static attribute. What\'s better? And why? 回答1: In general, static means "associated with the type itself, rather than an instance of the type." That means you can reference a static variable without having ever created an instances of the type, and any code referring to the variable is referring to the exact same data. Compare

Why is the String class declared final in Java?

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问题 From when I learned that the class java.lang.String is declared as final in Java, I was wondering why that is. I didn\'t find any answer back then, but this post: How to create a replica of String class in Java? reminded me of my query. Sure, String provides all the functionality I ever needed, and I never thought of any operation that would require an extension of class String, but still you\'ll never know what someone might need! So, does anyone know what the intent of the designers was

final keyword in method parameters [duplicate]

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问题 This question already has an answer here: Why should I use the keyword “final” on a method parameter in Java? 12 answers I often encounter methods which look like the following: public void foo(final String a, final int[] b, final Object1 c){ } What happens if this method is called without passing it final parameters. i.e. an Object1 that is later changed (so is not declared as final) can be passed to this method just fine 回答1: Java always makes a copy of parameters before sending them to

Why should I use the keyword “final” on a method parameter in Java?

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问题 I can\'t understand where the final keyword is really handy when it is used on method parameters. If we exclude the usage of anonymous classes, readability and intent declaration then it seems almost worthless to me. Enforcing that some data remains constant is not as strong as it seems. If the parameter is a primitive then it will have no effect since the parameter is passed to the method as a value and changing it will have no effect outside the scope. If we are passing a parameter by

When should one use final for method parameters and local variables?

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问题 I\'ve found a couple of references (for example) that suggest using final as much as possible and I\'m wondering how important that is. This is mainly in the the context of method parameters and local variables, not final methods or classes. For constants, it makes obvious sense. On one hand, the compiler can make some optimizations and it makes the programmer\'s intent clearer. On the other hand, it adds verbosity and the optimizations may be trivial. Is it something I should make an effort

Lambdas: local variables need final, instance variables don't

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In a lambda, local variables need to be final, but instance variables don't. Why so? The fundamental difference between a field and a local variable is that the local variable is copied when JVM creates a lambda instance. On the other hand, fields can be changed freely, because the changes to them are propagated to the outside class instance as well (their scope is the whole outside class, as Boris pointed out below). The easiest way of thinking about anonymous classes, closures and labmdas is from the variable scope perspective; imagine a copy constructor added for all local variables you

Lambdas: local variables need final, instance variables don't

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问题 In a lambda, local variables need to be final, but instance variables don\'t. Why so? 回答1: The fundamental difference between a field and a local variable is that the local variable is copied when JVM creates a lambda instance. On the other hand, fields can be changed freely, because the changes to them are propagated to the outside class instance as well (their scope is the whole outside class, as Boris pointed out below). The easiest way of thinking about anonymous classes, closures and

Why would one mark local variables and method parameters as “final” in Java? [closed]

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问题 In Java, you can qualify local variables and method parameters with the final keyword. public static void foo(final int x) { final String qwerty = \"bar\"; } Doing so results in not being able to reassign x and qwerty in the body of the method. This practice nudges your code in the direction of immutability which is generally considered a plus. But, it also tends to clutter up code with \"final\" showing up everywhere. What is your opinion of the final keyword for local variables and method

Does use of final keyword in Java improve the performance?

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问题 In Java we see lots of places where the final keyword can be used but its use is uncommon. For example: String str = \"abc\"; System.out.println(str); In the above case, str can be final but this is commonly left off. When a method is never going to be overridden we can use final keyword. Similarly in case of a class which is not going to be inherited. Does the use of final keyword in any or all of these cases really improve performance? If so, then how? Please explain. If the proper use of