test/langtools/tools/javac/jvm/ClassRefDupInConstantPoolTest.java

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/*
 * @test
 * @bug 8015927
 * @summary Class reference duplicates in constant pool
 * @clean ClassRefDupInConstantPoolTest ClassRefDupInConstantPoolTest$Duplicates
 * @run main ClassRefDupInConstantPoolTest
 */

import java.util.TreeSet;

import java.lang.classfile.*;
import java.lang.classfile.constantpool.*;

public class ClassRefDupInConstantPoolTest {
    public static void main(String[] args) throws Exception {
        ClassModel cls = ClassFile.of().parse(ClassRefDupInConstantPoolTest.class.
                                       getResourceAsStream("ClassRefDupInConstantPoolTest$Duplicates.class").readAllBytes());
        ConstantPool pool = cls.constantPool();

        int duplicates = 0;
        TreeSet<String> set = new TreeSet<>();
        for (PoolEntry pe : pool) {
            if (pe instanceof ClassEntry ce) {
                if (!set.add(ce.asInternalName())) {
                    duplicates++;
                    System.out.println("DUPLICATE CLASS REF " + ce.asInternalName());
                }
            }
        }
        if (duplicates > 0)
            throw new Exception("Test Failed");
    }

    class Duplicates {
        String concat(String s1, String s2) {
            return s1 + (s2 == s1 ? " " : s2);
        }
    }
}