如何将字符串转换为lambda表达式？-Howtoconvertastringtoalambdaexpression?

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Marko's comment on the question is correct. You can't read a bare Java lambda expression out of a file, since such an expression isn't defined without a target type provided by the context. For example, consider the following method declarations:

Marko对这个问题的评论是正确的。您无法从文件中读取裸Java lambda表达式,因为如果没有上下文提供的目标类型,则不会定义此类表达式。例如,请考虑以下方法声明:

void method1(BiFunction f) { ... }
void method2(BiFunction f) { ... }

Then in the following code,

然后在下面的代码中,

method1((x, y) -> x + y);
method2((x, y) -> x + y);

the two lambda expressions (x, y) -> x + y mean completely different things. For method1, the + operator is string concatenation, but for method2, it means integer addition.

两个lambda表达式(x,y) - > x + y表示完全不同的东西。对于method1,+运算符是字符串连接,但对于method2,它表示整数加法。

This is wandering a bit far afield from your question, but you can read and evaluate a lambda or function expression using a dynamic language. In Java 8 there is the Nashorn Javascript engine. So instead of attempting to read an evaluate a Java lambda expression, you could read and evaluate a Javascript function using Nashorn, called from Java.

这在你的问题上有点偏远,但你可以使用动态语言阅读和评估lambda或函数表达式。在Java 8中有Nashorn Javascript引擎。因此,您可以使用从Java调用的Nashorn来读取和评估Javascript函数,而不是尝试读取评估Java lambda表达式。

The following code takes a function in arg[0] and applies it to each subsequent, printing the results:

以下代码采用arg [0]中的函数并将其应用于每个后续函数,打印结果:

import java.util.function.Function;
import javax.script.*;

public class ScriptFunction {
    public static void main(String[] args) throws Exception {
        ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
        @SuppressWarnings("unchecked")
        Function
 
Still, you might find this technique useful if you have a need to evaluate expressions or functions read from a file.
 
但是,如果您需要评估从文件中读取的表达式或函数,您可能会发现此技术很有用。