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javaclinuxjava-native-interface

Calling Collections.sort via JNI

I am working on a JNI implementation using C and try to sort a list of type java/lang/List using java/util/Collections sort method with a Comparator. To get the descriptor signatures I mainly use javap.

In this case javap does not show any descriptor for the sort methods. All I get is 

$ javap -s -p java.util.Collections | grep -i sort
public static <T extends java.lang.Comparable<? super T>> void sort(java.util.List<T>);
public static <T> void sort(java.util.List<T>, java.util.Comparator<? super T>);
...

In the JNI code, I use

// Get Collections class
jclass collections_clazz = (*(px->env))->FindClass(px->env, "java/util/Collections");
if (!collections_clazz) ...

// Get sort method
jmethodID sort_mid = (*(px->env))->GetStaticMethodID(px->env, collections_clazz, 
    "sort", "(Ljava/lang/List;Ljava/util/Comparator;)V");
if (!sort_mid) ...

In my case sort_mid is false (or NULL). The signature I use with GetStaticMethodID is a rough guess. I have to admit I am not deep into Java, but its enough to use with JNI though.

I am using jdk1.8.0_31 with this project.

Could anybody give me a hint whats the issue here? What I am missing?

Thanks in advance for the help!

Solution

  • Perhaps confusingly, standard classes like List are not in java.lang or even java.collections but java.util

    You need Ljava/util/List