final

问题 I was looking at another question about final variables and noticed that you can declare final variables without initializing them (a blank final variable). Is there a reason it is desirable to do this, and when is it advantageous? 回答1: This is useful to create immutable objects: public class Bla { private final Color color; public Bla(Color c) {this.color = c}; } Bla is immutable (once created, it can't change because color is final). But you can still create various Blas by constructing

问题 I want a class that I can create instances of with one variable unset (the id ), then initialise this variable later, and have it immutable after initialisation . Effectively, I'd like a final variable that I can initialise outside of the constructor. Currently, I'm improvising this with a setter that throws an Exception as follows: public class Example { private long id = 0; // Constructors and other variables and methods deleted for clarity public long getId() { return id; } public void

问题 What is difference between in the following statements String name = "Tiger"; final String name ="Tiger"; Although the String class is final class, why do we need to create a String "CONSTANT" variable as final? 回答1: final in this context means that the variable name can only be assigned once. Assigning a different String object to it again results in a compile error. I think the source of the confusion here is that the final keyword can be used in several different contexts: final class: The

问题 This question already has answers here : Why would one mark local variables and method parameters as “final” in Java? [closed] (12 answers) Closed 3 years ago . I was wondering is there any usability of using final local variables. Variables are not overridden anyway when inheritance comes into picture. For example a simple code as below public static void main(String args[]) { final String data = "Hello World!"; System.out.println(data); } The example is quite simple one and may not be a

问题 This question already has answers here : Cannot refer to a non-final variable inside an inner class defined in a different method (20 answers) Closed 6 years ago . So i have a JList and i am trying to use it inside of a JButton s actionPerformed method and it is asking me to make the JList final why is that, below is a code snippet public SomeClass() { btnNewButton.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { list.clearSelection(); }}); } I don't

问题 how it can be possible that we can initialize the final variable of the class at the creation time of the object ? Anybody can explain it how is it possible ? ... 回答1: You must initialize a final variable once and only once. There are three ways to do that for an instance variable: in the constructor in an instance initialization block. when you declare it Here is an example of all three: public class X { private final int a; private final int b; private final int c = 10; { b = 20; } public X

问题 I've come across a class that includes multiple uses of a string literal, "foo". What I'd like to know, is what are the benefits and impact (in terms of object creation, memory usage and speed) of using this approach instead of declaring the String as final and replacing all the literals with the final variable? For example (although obviously not a real word usage): private static final String FINAL_STRING = "foo"; public void stringPrinter(){ for(int i=0;i<10;i++){ System.out.println(FINAL

问题 Is it beneficial to make private methods final? Would that improve performance? I think "private final" doesn't make much sense, because a private method cannot be overridden. So the method lookup should be efficient as when using final. And would it be better to make a private helper method static (when possible)? What's best to use? private Result doSomething() private final Result doSomething() private static Result doSomething() private static final Result doSomething() 回答1: Adding final

问题 Is it beneficial to make private methods final? Would that improve performance? I think "private final" doesn't make much sense, because a private method cannot be overridden. So the method lookup should be efficient as when using final. And would it be better to make a private helper method static (when possible)? What's best to use? private Result doSomething() private final Result doSomething() private static Result doSomething() private static final Result doSomething() 回答1: Adding final

问题 When I compile this snippet. public class InternTest { public static void main(String...strings ){ final String str1="str"; final String str2="ing"; String str= str1+str2; } } Which produces the following byte code public static void main(java.lang.String...); flags: ACC_PUBLIC, ACC_STATIC, ACC_VARARGS Code: stack=1, locals=4, args_size=1 0: ldc #16 // String str 2: astore_1 3: ldc #18 // String ing 5: astore_2 6: ldc #20 // String string 8: astore_3 9: return so string literal "string" is