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  1. JDK
  2. JDK-8226720

Unexpected compiler behaviors on generic class's non-static method with Map para

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    • Subcomponent:
    • CPU:
      generic
    • OS:
      generic

      Description

      ADDITIONAL SYSTEM INFORMATION :
      OS: CentOS Linux release 7.2.1511 (Core)
      # uname -a
      Linux SZE-L0163338 3.10.0-862.9.1.el7.x86_64 #1 SMP Mon Jul 16 16:29:36 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

      Java: have tried 12.0.1, and 14 early access:
      # ./java -version
      java version "12.0.1" 2019-04-16
      Java(TM) SE Runtime Environment (build 12.0.1+12)
      Java HotSpot(TM) 64-Bit Server VM (build 12.0.1+12, mixed mode, sharing)

      # java -version
      openjdk version "14-ea" 2020-03-17
      OpenJDK Runtime Environment (build 14-ea+2-29)
      OpenJDK 64-Bit Server VM (build 14-ea+2-29, mixed mode, sharing)


      A DESCRIPTION OF THE PROBLEM :
      The following compiler error is expected on line 9. In fact, compilation is succeed after line 14-16 has been commented, and then it failed in execution because of ClassCastException as expected.

      Expected compiler error examples:
      CallGGNSGM.java:14: error: incompatible types: Map<String,String> cannot be converted to Map<String,Object>
              GGSGM.call(map);
                         ^
      CallGGNSGM.java:15: error: incompatible types: Map<String,String> cannot be converted to Map<String,Object>
              (new NSGM()).call(map);
                                ^
      CallGGNSGM.java:16: error: incompatible types: Map<String,String> cannot be converted to Map<String,Object>
              SGM.call(map);
                       ^

      Main class (CallGGNSGM) implementation:

      import java.util.HashMap;
      import java.util.Map;

      public class CallGGNSGM {
          public static void main(String[] args) {
              Map<String, String> map = new HashMap();
              map.put("k", "v");
              System.out.println("CallGGSGM try gg_instantiated_gm");
              (new GGNSGM()).call(map); //Compiler error(as lines 14-16) expected here
              System.out.println(map);
              for (Map.Entry<String, String> entry : map.entrySet()) {
                  System.out.println(entry.getKey() + " : " + entry.getValue());
              }
      // GGSGM.call(map);
      // (new NSGM()).call(map);
      // SGM.call(map);
          }
      }

      GGNSGM:
      import java.util.Map;

      public class GGNSGM<T> {
          public void call(Map<String, Object> map) {
              System.out.println("call gg_instantiated_gm_map<String, Object> " + map);
              map.put("k2", new Integer(1));
          }
      }

      GGSGN:
      import java.util.Map;

      public class GGSGM<T> {
          public static void call(Map<String, Object> map) {
              System.out.println("call gg_static_gm_map<String, Object> " + map);
          }
      }

      NSGM:
      import java.util.Map;

      public class NSGM {
          public void call(Map<String, Object> map) {
              System.out.println("call instantiated_gm_map<String, Object> " + map);
          }
      }

      SGM:
      import java.util.Map;

      public class SGM {
          public static void call(Map<String, Object> map) {
              System.out.println("call static_gm_map<String, Object> " + map);
          }
      }


      STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
      Try compile the attached source files: CallGGNSGM.java, GGNSGM.java, GGSGM.java, NSGM.java, SGM.java, and then launch CallGGNSGM.class

      EXPECTED VERSUS ACTUAL BEHAVIOR :
      EXPECTED -
      Compiler error expected while compiling.
      ACTUAL -
      Compilation succeeded, and then failed in execution because of ClassCastException.

      ---------- BEGIN SOURCE ----------
      Main class (CallGGNSGM) implementation:

      import java.util.HashMap;
      import java.util.Map;

      public class CallGGNSGM {
          public static void main(String[] args) {
              Map<String, String> map = new HashMap();
              map.put("k", "v");
              System.out.println("CallGGSGM try gg_instantiated_gm");
              (new GGNSGM()).call(map); //Compiler error(as lines 14-16) expected here
              System.out.println(map);
              for (Map.Entry<String, String> entry : map.entrySet()) {
                  System.out.println(entry.getKey() + " : " + entry.getValue());
              }
      // GGSGM.call(map);
      // (new NSGM()).call(map);
      // SGM.call(map);
          }
      }

      GGNSGM:
      import java.util.Map;

      public class GGNSGM<T> {
          public void call(Map<String, Object> map) {
              System.out.println("call gg_instantiated_gm_map<String, Object> " + map);
              map.put("k2", new Integer(1));
          }
      }

      GGSGN:
      import java.util.Map;

      public class GGSGM<T> {
          public static void call(Map<String, Object> map) {
              System.out.println("call gg_static_gm_map<String, Object> " + map);
          }
      }

      NSGM:
      import java.util.Map;

      public class NSGM {
          public void call(Map<String, Object> map) {
              System.out.println("call instantiated_gm_map<String, Object> " + map);
          }
      }

      SGM:
      import java.util.Map;

      public class SGM {
          public static void call(Map<String, Object> map) {
              System.out.println("call static_gm_map<String, Object> " + map);
          }
      }
      ---------- END SOURCE ----------

      FREQUENCY : always


        Attachments

        1. CallGGNSGM.java
          0.6 kB
          Fairoz Matte
        2. GGNSGM.java
          0.3 kB
          Fairoz Matte
        3. GGSGN.java
          0.2 kB
          Fairoz Matte
        4. NSGM.java
          0.2 kB
          Fairoz Matte
        5. SGM.java
          0.2 kB
          Fairoz Matte

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            Assignee:
            Unassigned Unassigned
            Reporter:
            webbuggrp Webbug Group
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              Dates

              Created:
              Updated: