DynamicCallSiteDesc resolveCallSiteDesc(Lookup) in Java

resolveCallSiteDesc(Lookup): This method is available in the java.lang.constant.DynamicCallSiteDesc class of Java.

Syntax:

CallSite java.lang.constant.DynamicCallSiteDesc.resolveCallSiteDesc(Lookup lookup) throws Throwable

This method takes one argument. This method reflectively invokes the bootstrap method with the specified arguments and returns the resulting CallSite

Parameters: One parameter is required for this method.

lookup: The MethodHandles.Lookup is used to resolve class names.

Returns: the CallSite.

Throws:

1. Throwable - if any exception is thrown by the bootstrap method

Approach

Java

package com.DynamicCallSiteDesc;

import java.lang.constant.ClassDesc;
import java.lang.constant.DirectMethodHandleDesc;
import java.lang.constant.DynamicCallSiteDesc;
import java.lang.constant.MethodTypeDesc;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodHandles.Lookup;

public class DynamicCallSiteDescresolveCallSiteDesc {
    public static void main(String[] args) throws Throwable {

        DirectMethodHandleDesc desc = new DirectMethodHandleDesc() {

            @Override
            public Object resolveConstantDesc(Lookup lookup) throws ReflectiveOperationException {
                return "Hello";

            }

            @Override
            public MethodTypeDesc invocationType() {
                return MethodTypeDesc.of(ClassDesc.of("name"), ClassDesc.of("name"));
            }

            @Override
            public int refKind() {

                return 0;
            }

            @Override
            public ClassDesc owner() {

                return ClassDesc.of("name");
            }

            @Override
            public String methodName() {

                return "name";
            }

            @Override
            public String lookupDescriptor() {

                return "LookupDescriptor";
            }

            @Override
            public Kind kind() {
                return Kind.CONSTRUCTOR;
            }

            @Override
            public boolean isOwnerInterface() {
                return true;
            }
        };
        DynamicCallSiteDesc dynamicCallSiteDesc = DynamicCallSiteDesc.of(desc,
                MethodTypeDesc.of(ClassDesc.of("name"), ClassDesc.of("name")));

        MethodHandles.Lookup lookup = MethodHandles.lookup();

        System.out.println(dynamicCallSiteDesc.resolveCallSiteDesc(lookup));
    }
}

Output:

Exception in thread "main" java.lang.ClassCastException: class java.lang.String cannot be cast to class java.lang.invoke.MethodHandle (java.lang.String and java.lang.invoke.MethodHandle are in module java.base of loader 'bootstrap')
	at java.base/java.lang.constant.DynamicCallSiteDesc.resolveCallSiteDesc(DynamicCallSiteDesc.java:234)
	at com.DynamicCallSiteDesc.DynamicCallSiteDescresolveCallSiteDesc.main(DynamicCallSiteDescresolveCallSiteDesc.java:65)

Some other methods of DynamicCallSiteDesc

bootstrapArgs(): This method returns ConstantDescs describing the bootstrap arguments for the invoke dynamic.

bootstrapMethod(): This method returns a MethodHandleDesc describing the bootstrap method for the invoke dynamic.

equals(Object): This method compares the specified object with this descriptor for equality.

hashCode(): This method returns a hash code value for the object.

invocationName(): This method returns the invocation name that would appear in the NameAndType operand of the invoke dynamic.

invocationType(): This method returns a MethodTypeDesc describing the invocation type that would appear in the NameAndType operand of the invoke dynamic.

DynamicCallSiteDesc.of(DirectMethodHandleDesc, MethodTypeDesc): This method creates a nominal descriptor for an invoke dynamic call site whose bootstrap method has no static arguments and for which the name parameter is ConstantDescs.DEFAULT_NAME.

DynamicCallSiteDesc.of(DirectMethodHandleDesc, String, MethodTypeDesc): This method creates a nominal descriptor for an invokes dynamic call site whose bootstrap method has no static arguments.

DynamicCallSiteDesc.of(DirectMethodHandleDesc, String, MethodTypeDesc, ConstantDesc...): This method creates a nominal descriptor for an invoke dynamic call site.

resolveCallSiteDesc(Lookup): This method reflectively invokes the bootstrap method with the specified arguments and returns the resulting CallSite.

toString(): This method returns a compact textual description of this call site description, including the bootstrap method, the invocation name and type, and the static bootstrap arguments.

withArgs(ConstantDesc...): This method returns a nominal descriptor for an invoke dynamic call site whose bootstrap method, name, and invocation type are the same as this one, but with the specified bootstrap arguments.

withNameAndType(String, MethodTypeDesc): This method returns a nominal descriptor for an invoke dynamic call site whose bootstrap and bootstrap arguments are the same as this one, but with the specified invocationName and invocation invocationType.