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This article shows you how to reduce NPE, the content is concise and easy to understand, can definitely brighten your eyes, through the detailed introduction of this article, I hope you can get something.

Programmer, if the system suddenly reports a null pointer exception, you must be as embarrassed as swallowing a fly.

So how to reduce NPE in the daily development process?

If the null value is returned in the status quo of the question answer, there will be a large number of null pointer exceptions to improve the return value of the method, and reduce the null pointer exception to realize that the path method returns an empty set or an empty array.

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Background

The following methods seem to be common.

Private final List chessesInStock=... public List getCheeses () {return cheesesInStock.isEmpty ()? null:new ArrayList (cheesesInStock);}

If you don't have cheese available when you buy cheese, there seems to be no reason to specifically point out this scenario.

But if you do, the client needs to add additional code to handle situations where null values may be returned. The sample code is as follows:

List cheeses = shop.getCheeses (); if (cheses! = null & & cheeses.contains (Cheese.STILTON)) {System.out.println ("jolly good");}

Each method that returns a null value uses the above treatment and should be replaced with an empty collection or empty array.

This is an erroneous trend because programmers may forget to write special code to handle null values returned.

This error can take a long time because such a method usually returns one or more objects.

The argument of not returning an empty set empty array

Replacing the return null value with an empty container also complicates the implementation of the method.

It is often argued that it is better to return a null value than an empty collection because it consumes performance to create an empty container.

This argument is wrong for two reasons:

First, there is no need to worry about performance unless there is evidence that creating an empty container is detrimental to performance.

Second, you can return an empty collection or array without creating them.

Returns an empty collection

The following is a typical code that returns a possible empty collection, which is usually what you need.

Public List getCheeses () {return new ArrayList (cheeseInStock);}

There is no evidence that creating an empty collection harms performance, you can return the same immutable empty collection to avoid creating an empty collection. Because immutable objects can be freely shared, here is the code to use.

Requirements scenario code null ListCollections.emptyList () empty SetCollections.emptySet () empty MapCollections.emptyMap ()

But remember, these operations are just optimized and rarely called, and if you think you need it, compare performance before and after the call to make sure it's really useful.

Public List getCheeses () {return cheesesInStock.isEmpty ()? Collections.emptyList (): new ArrayList (cheesesInStock);} returns an empty array

The scenario of using an array is the same as a collection. Never return a null value. You should return an array of 0 bits in length. Often, you should simply return an array of appropriate length, perhaps 0 in length.

Notice that we pass an array of length 0 to the toArray method to represent the expected return type

Public Cheese [] getCheeses () {return cheesesInStock.toArray (new Cheese [0]);}

If you think creating an array of length 0 will degrade performance, you can return the same array of length 0, because all arrays of length 0 are immutable

Private static final Cheese [] EMPTY_ARRAY= new Cheese [0]; public Cheeses [] getCheeses () {return cheesesInStock.toArray (EMPTY_ARRAY);}

In the optimized version, we passed the same empty array to each toArray call, this array will be returned from the getCheeses, whether the cheesesInStock is empty or not, do not expect pre-allocated array to improve performance, studies have shown that this is counterproductive.

Return cheesesInStock.toArray (new Cheese [cheesesInStock.size ()])

If you can only remember one sentence: return an empty collection or array instead of a null value.

Returning null values will make your API more difficult to use and more error-prone, with no performance advantage.

The above content is how to reduce NPE. Have you learned any knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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