如何获取类(Java)中所有方法的方法引用? [英] How to get Method Reference for all methods in a class (Java)?
问题描述
方法参考可以作为 Class :: Method
获得。但是如何获取类的所有方法的方法引用?
Method Reference for a specific method in Java 8 can be obtained as Class::Method
. But how to get the method reference of all methods of a class?
所有需要的方法都有不同的方法名称,但相同的类型签名。此外,这些方法的名称在之前是未知。
All the desired methods have different method names, but the same type signature. Also, the names of the methods is not known before hand.
示例:
class Test {
public static double op0(double a) { ... }
public static double op1(double a) { ... }
public static double op2(double a) { ... }
public static double op3(double a) { ... }
public static double op4(double a) { ... }
}
对已知方法的方法引用 op0
可以获得:
The method reference to a known method op0
can be obtained as:
DoubleFunction<Double> f = Test::op0;
但是,如何获取类中所有方法的方法引用?
But, how to get the method references of all methods in the class?
推荐答案
没有反射可行的解决方案,因为现有方法的动态发现是反射操作。但是,一旦发现方法并创建了方法引用实例(或其动态等价物),代码的实际调用将在没有反射的情况下运行:
There is no solution that works without Reflection as the dynamic discovery of existing methods is a reflective operation. However, once methods are discovered and a method reference instance (or the dynamic equivalent of it) has been created, the actual invocation of the code runs without Reflection:
class Test {
public static double op0(double a) { ... }
public static double op1(double a) { ... }
public static double op2(double a) { ... }
public static double op3(double a) { ... }
public static double op4(double a) { ... }
static final Map<String, DoubleUnaryOperator> OPS;
static {
HashMap<String, DoubleUnaryOperator> map=new HashMap<>();
MethodType type=MethodType.methodType(double.class, double.class);
MethodType inT=MethodType.methodType(DoubleUnaryOperator.class);
MethodHandles.Lookup l=MethodHandles.lookup();
for(Method m:Test.class.getDeclaredMethods()) try {
if(!Modifier.isStatic(m.getModifiers())) continue;
MethodHandle mh=l.unreflect(m);
if(!mh.type().equals(type)) continue;
map.put(m.getName(), (DoubleUnaryOperator)LambdaMetafactory.metafactory(
l, "applyAsDouble", inT, type, mh, type).getTarget().invokeExact());
} catch(Throwable ex) {
throw new ExceptionInInitializerError(ex);
}
OPS=Collections.unmodifiableMap(map);
}
}
初始化类后,您可以调用特殊操作没有使用 OPS.get(name).applyAsDouble(doubleValue)
或使用调用所有操作,例如
Once the class has been initialized, you can invoke a particular op without Reflection using OPS.get(name).applyAsDouble(doubleValue)
or invoke all ops using, e.g.
OPS.forEach((name,op)-> System.out.println(name+'('+42+") => "+op.applyAsDouble(42)));
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