final

What does final do in the following Java expression? catch (final SomeExceptionType e) It basically means: Catch "SomeExceptionType" into the variable "e" with the promise that we won't assign a different exception to "e" during the processing of the exception. Mostly this is overkill, as if I'm catching an exception into a temporary variable name (e only is valid for the exception handling block), I don't have to police myself so strictly as to not trust myself to assign a different (possibly created) exception to the same variable name. That said, perhaps this block is heavily maintained by

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() Adding final to methods does not improve performance with Sun HotSpot. Where final could be added, HotSpot will notice

/* * final:是一个关键字,最后的,最终的.被final修饰的内容是不能再被改变的. * * 可以修饰的内容: * 1.类:final修饰的类不能有子类 * 2.成员变量:变量是一个终值,不能再被改变.所以在定义时必须先手动给一个值. * 3.局部变量:被final修饰的局部变量是一个终值,不能再被改变 * 4.方法:final修饰的方法不允许重写 * 5.空白final----了解 */ public class Demo1 { public static void main(String[] args) { Ainmal ainmal = new Ainmal(); } } class Ainmal{ //这里的红色不是初始化,是赋值 //当构造方法执行的时候,会立刻对属性进行初始化,引用类型赋值成null.接下来才会去读取红色这个值并赋值给color String color = "红色"; final String name = "冰冰" ;//2.成员变量:变量是一个终值,不能再被改变.所以在定义时必须先手动给一个值. public Ainmal() { //对自己的属性进行初始化 super();//调用父类的构造方法 //做自己的事情 System.out.println("自己的功能"); //因为name已经是一个final的,不能再被改变. //name

Could you please clarify that why final keyword is required before class when we are making it an immutable one. I mean, if we declare all of it's attributes as private and final, then also it is an immutable class, isn't it? Sorry if the question seems easy, but i am truly confused about it. Help me out. Editted: I know that a class declared final can't be subclassed.. But if each attribute is private and final then what difference does that make? Jon Skeet As stacker says, final makes sure the class isn't subclassed. That's important so that any code which is relying on its immutability can

I have a program like this: class Test { final int x; { printX(); } Test() { System.out.println("const called"); } void printX() { System.out.println("Here x is " + x); } public static void main(String[] args) { Test t = new Test(); } } If I try to execute it, i am getting compiler error as : variable x might not have been initialized based on java default values i should get the below output right?? "Here x is 0". Will final variables have dafault values? if I change my code like this, class Test { final int x; { printX(); x = 7; printX(); } Test() { System.out.println("const called"); } void

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 already there in the constant pool which gets pushed 6: ldc #20 // String string on stack at this line.

I have an class defining an immutable value type that I now need to serialize. The immutability comes from the final fields which are set in the constructor. I've tried serializing, and it works (surprisingly?) - but I've no idea how. Here's an example of the class public class MyValueType implements Serializable { private final int value; private transient int derivedValue; public MyValueType(int value) { this.value = value; this.derivedValue = derivedValue(value); } // getters etc... } Given that the class doesn't have a no arg constructor, how can it be instantiated and the final field set?