boxing | 易学教程

Why do we need boxing and unboxing in C#?

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问题 Why do we need boxing and unboxing in C#? I know what boxing and unboxing is, but I can\'t comprehend the real use of it. Why and where should I use it? short s = 25; object objshort = s; //Boxing short anothershort = (short)objshort; //Unboxing 回答1: Why To have a unified type system and allow value types to have a completely different representation of their underlying data from the way that reference types represent their underlying data (e.g., an int is just a bucket of thirty-two bits

Convert an array of primitive longs into a List of Longs

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问题 This may be a bit of an easy, headdesk sort of question, but my first attempt surprisingly completely failed to work. I wanted to take an array of primitive longs and turn it into a list, which I attempted to do like this: long[] input = someAPI.getSomeLongs(); List<Long> inputAsList = Arrays.asList(input); //Total failure to even compile! What\'s the right way to do this? 回答1: I found it convenient to do using apache commons lang ArrayUtils (JavaDoc, Maven dependency) import org.apache

How to convert int[] into List<Integer> in Java?

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问题 How do I convert int[] into List<Integer> in Java? Of course, I\'m interested in any other answer than doing it in a loop, item by item. But if there\'s no other answer, I\'ll pick that one as the best to show the fact that this functionality is not part of Java. 回答1: There is no shortcut for converting from int[] to List<Integer> as Arrays.asList does not deal with boxing and will just create a List<int[]> which is not what you want. You have to make a utility method. int[] ints = {1, 2, 3};

Integer wrapper class and == operator - where is behavior specified? [duplicate]

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This question already has an answer here: Integer wrapper objects share the same instances only within the value 127? [duplicate] 5 answers Integer integer1 = 127; Integer integer2 = 127; System.out.println(integer1 == integer2);//true integer1 = 128; integer2 = 128; System.out.println(integer1 == integer2);//false I found it returns == (if it is) under the range of -128 - 127 , why is there such specification ? Because of this code in Integer.valueOf(int) : public static Integer valueOf(int i) { if(i >= -128 && i <= IntegerCache.high) return IntegerCache.cache[i + 128]; else return new

What is boxing and unboxing and what are the trade offs?

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I'm looking for a clear, concise and accurate answer. Ideally as the actual answer, although links to good explanations welcome. Boxed values are data structures that are minimal wrappers around primitive types *. Boxed values are typically stored as pointers to objects on the heap . Thus, boxed values use more memory and take at minimum two memory lookups to access: once to get the pointer, and another to follow that pointer to the primitive. Obviously this isn't the kind of thing you want in your inner loops. On the other hand, boxed values typically play better with other types in the

Convert an array of primitive longs into a List of Longs

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This may be a bit of an easy, headdesk sort of question, but my first attempt surprisingly completely failed to work. I wanted to take an array of primitive longs and turn it into a list, which I attempted to do like this: long[] input = someAPI.getSomeLongs(); List<Long> inputAsList = Arrays.asList(input); //Total failure to even compile! What's the right way to do this? I found it convenient to do using apache commons lang ArrayUtils ( JavaDoc , Maven dependency ) import org.apache.commons.lang3.ArrayUtils; ... long[] input = someAPI.getSomeLongs(); Long[] inputBoxed = ArrayUtils.toObject