标签:java lambda functional-interface
参见英文答案 > What is a Java 8 Lambda Expression Compiled to? 1个
我有以下方法调用,其中我传递一个lambda表达式.是否在这里隐式实例化了一个类?
printStudents(
roster,
(Student s) -> s.getGender() == Student.Sex.MALE
&& s.getAge() >= 18
&& s.getAge() <= 25
);
方法签名:
printStudents(List<Student> roster, CheckStudent checkstudet)
interface CheckStudent {
boolean test(Student s);
}
编辑
有些人建议我重构代码,但同样的问题出现了.
CheckStudent checkStudent = (Student s) -> s.getGender() == Student.Sex.MALE && s.getAge() >= 18 && s.getAge() <= 25;
是否在作业的右侧实例化了一个班级(我不是指学生班级)?
解决方法:
lambda表达式的值是对类实例的引用.所以,实际上,是的,正在创建一个类的实例.看看文档说的内容:
At run time, evaluation of a lambda expression is similar to
evaluation of a class instance creation expression, insofar as normal
completion produces a reference to an object.
但是,除了我们可以“看到”之外还有更多.引擎盖下有许多优化.根据某些因素,例如,可以再次使用先前创建的对象.这意味着不需要在lambda表达式的每个评估上分配新对象.我们来看看文档:
Evaluation of a lambda expression is distinct from execution of the
lambda body. Either a new instance of a class with the properties below is
allocated and initialized, or an existing instance of a class with the
properties below is referenced.[…]
These rules are meant to offer flexibility to implementations of the
Java programming language, in that:
A new object need not be allocated on every evaluation.
Objects produced by different lambda expressions need not belong to different classes (if the bodies are identical, for example).
Every object produced by evaluation need not belong to the same class (captured local variables might be inlined, for example).
If an “existing instance” is available, it need not have been created at a previous lambda evaluation (it might have been allocated
during the enclosing class’s initialization, for example).
您可能已经注意到,这是一个复杂的主题.有关更深入的理解,请参阅TheJava®语言规范,第“15.27.4. Run-time Evaluation of Lambda Expressions”章.
标签:java,lambda,functional-interface 来源: https://codeday.me/bug/20190705/1387705.html
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