Created
March 20, 2017 15:58
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How to get Method Reference for all methods in a class (Java)?
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import java.lang.invoke.LambdaMetafactory; | |
import java.lang.invoke.MethodHandle; | |
import java.lang.invoke.MethodHandles; | |
import java.lang.invoke.MethodType; | |
import java.lang.reflect.Method; | |
import java.lang.reflect.Modifier; | |
import java.util.Collections; | |
import java.util.HashMap; | |
import java.util.Map; | |
import java.util.function.DoubleUnaryOperator; | |
class Test { | |
public static double op0(double a) { | |
return a; | |
} | |
public static double op1(double a) { | |
return a; | |
} | |
public static double op2(double a) { | |
return a; | |
} | |
public static double op3(double a) { | |
return a; | |
} | |
public static double op4(double a) { | |
return 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); | |
} | |
public static void main(String args[]) { | |
OPS.forEach((name, op) -> System.out.println(name + '(' + 42 + ") => " + op.applyAsDouble(42))); | |
} | |
} |
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