語(yǔ)法糖是啥？語(yǔ)法糖沒(méi)有一個(gè)官方的定義(或者說(shuō)定義相當(dāng)寬泛)，更像是一種觀念：任何讓你寫著爽、但是實(shí)際發(fā)生的和你看到的不一樣的東西都可以“被認(rèn)為”是語(yǔ)法糖。例如最常見的Integer和int的自動(dòng)裝拆箱操作背后就是語(yǔ)法糖。看上去你在寫

Integer i = 1234;

int j = new Integer(2345);

編譯器在背后偷偷摸摸地幫你加了一些料：

Integer i = Integer.valueOf(1234); // 實(shí)際生成的字節(jié)碼的等價(jià)代碼

int j = new Integer(2345).intValue();

在Java代碼的編譯過(guò)程中有一步叫做“解語(yǔ)法糖”(desugar)，就是做這種偷偷摸摸的事情的。

在JDK的源代碼里搜索"lambda desugar"我們可以很容易找到相關(guān)的解語(yǔ)法糖代碼：https://github.com/frohoff/jdk8u-jdk/blob/master/src/share/classes/java/lang/invoke/LambdaMetafactory.java#L181-L191?github.comhttps://github.com/openjdk/jdk/blob/master/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/LambdaToMethod.java#L81?github.com

/**

* This pass desugars lambda expressions into static methods

*

*

This is NOT part of any supported API.

* If you write code that depends on this, you do so at your own risk.

* This code and its internal interfaces are subject to change or

* deletion without notice.

*/

public class LambdaToMethod extends TreeTranslator {這個(gè)pass(類似于“一趟掃描”的意思，在生成抽象語(yǔ)法樹的過(guò)程中，編譯器可能要進(jìn)行多趟掃描)將lambda表達(dá)式解語(yǔ)法糖成為靜態(tài)方法。

* @apiNote These linkage methods are designed to support the evaluation

* of lambda expressions and method references in the Java

* Language. For every lambda expressions or method reference in the source code,

* there is a target type which is a functional interface. Evaluating a lambda

* expression produces an object of its target type. The recommended mechanism

* for evaluating lambda expressions is to desugar the lambda body to a method,

* invoke an invokedynamic call site whose static argument list describes the

* sole method of the functional interface and the desugared implementation

* method, and returns an object (the lambda object) that implements the target

* type. (For method references, the implementation method is simply the

* referenced method; no desugaring is needed.)……對(duì)Iambda表達(dá)式求值的過(guò)程會(huì)產(chǎn)生一個(gè)對(duì)應(yīng)的目標(biāo)類型(函數(shù)接口)的對(duì)象。對(duì)于每個(gè)lambda表達(dá)式的求值，推薦的方法是將lambda方法體解語(yǔ)法糖成為一個(gè)方法……

所以，不管你覺得是不是，也不管我覺得是不是，OpenJDK的實(shí)現(xiàn)認(rèn)為它是。

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