primitive

问题 I'm trying to create some Java classes, that should work with either float or double numbers (for simulation purposes I am required to support both). The classes need to do some basic arithmetic and also require use of trigonometric functions (sin, cos, atan2). I tried to do a generic approach. As Java does not allow primitive types in generics and MyClass<T extends Number> does indeed allow Double and Float, but makes basic arithmetic impossible, I build a wrapper class around Double and

问题 I'm trying to create some Java classes, that should work with either float or double numbers (for simulation purposes I am required to support both). The classes need to do some basic arithmetic and also require use of trigonometric functions (sin, cos, atan2). I tried to do a generic approach. As Java does not allow primitive types in generics and MyClass<T extends Number> does indeed allow Double and Float, but makes basic arithmetic impossible, I build a wrapper class around Double and

来源： https://stackoverflow.com/questions/43644203/why-in-one-case-multiplying-big-numbers-gives-a-wrong-result

问题 This question already has answers here : Does == actually work the same or different when comparing two primitives vs two Objects in Java? (2 answers) Closed 5 months ago . In java the "==" operator compares values for primitive types and compares the reference to the objects location in memory for reference types. For example: Primitive Types int x = 5; int y = 5; System.out.println(x == y); //true Reference Types String stringOne = new String("Hello"); String stringTwo = new String("Hello")

问题 I'm trying to understand how async/await works in conjunction together with promises. Code async function latestTime() { const bl = await web3.eth.getBlock('latest'); console.log(bl.timestamp); // Returns a primitive console.log(typeof bl.timestamp.then == 'function'); //Returns false - not a promise return bl.timestamp; } const time = latestTime(); // Promise { <pending> } Issue As far as I understand, await should be blocking and in the code above it seemingly blocks returning an object bl

问题 Alright, I've been programming in Java for the better part of three years, now, and consider myself very experienced. However, while looking over the Java SE source code, I ran into something I didn't expect: in class Double : public static final double MIN_NORMAL = 0x1.0p-1022; // 2.2250738585072014E-308 public static final double MIN_VALUE = 0x0.0000000000001P-1022; // 4.9e-324 I did not expect this and can't find out what it means. If you don't know, I'm referring to the p and P that are

问题 I'm trying to convert 2D list to a 2D int array. However, it seems I can only collect objects, not primitives. When I do: data.stream().map(l -> l.stream().toArray(int[]::new)).toArray(int[][]::new); I get the compile-time error Cannot infer type argument(s) for <R> map(Function<? super T,? extends R>) . However, if I change int[] to Integer[] , it compiles. How can I get it to just use int ? 回答1: Use mapToInt method to produce a stream of primitive integers: int[][] res = data.stream().map(l

问题 For instance, there’s an integer column in a database table. Then in java model, it can be mapped both as primitive int and Integer . My question is what's difference between the int and Integer in this case? And performance concern? Thanks! 回答1: I tend to avoid using primitives. This is especially true for the Id attribute. This makes it possible to detect a not yet set value by testing for null . If using Java 5 or above, auto-boxing takes away the pain (and is not a performance concern).

问题 This question already has answers here : Why does Java implicitly (without cast) convert a `long` to a `float`? (4 answers) Closed 4 years ago . if you call the following method of Java void processIt(long a) { float b = a; /*do I have loss here*/ } do I have information loss when I assign the long variable to the float variable? The Java language Specification says that the float type is a supertype of long . 回答1: Yes, this is possible: if only for the reason that float has too few

问题 This question already has answers here : How to determine that a JavaScript function is native (without testing '[native code]') (2 answers) Closed 2 years ago . I want to use javascript's Proxy objects to augment a data structure with a bit of additional logging. While doing so, I noticed a problem: simpleProxy = new Proxy(new Number(4), {}) simpleProxy.valueOf(); // TypeError: valueOf method called on incompatible Proxy The error makes sense to me. valueOf is invoked with the this object