java 10 compilaton Null Pointer Exception

Akshay Darekar :

I recently installed jdk10. I was doing normal code and it is not working.

Am I doing something wrong here? Please see the code and Exception stacktrace. As far as I understand there should be no reason for such behaviour.

import com.bean.College;

public class Student {

    interface Club {
        <T> T get(College<T> key);
    }

    private Club club;

    Student() {
        Object obj = club.get(new College<>() {});
    }
}

The imported College class is:

public class College<T> {
    int id;
    protected College() {
    }

    College(int id){
        this.id=id;
    }
} 

On compiling this the javac compiler crashes with the following stacktrace:

java.lang.NullPointerException
        at jdk.compiler/com.sun.tools.javac.comp.Flow$FlowAnalyzer.visitApply(Flow.java:1233)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1634)
        at jdk.compiler/com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:396)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$FlowAnalyzer.visitVarDef(Flow.java:987)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCVariableDecl.accept(JCTree.java:956)
        at jdk.compiler/com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:396)
        at jdk.compiler/com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:57)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$FlowAnalyzer.visitBlock(Flow.java:995)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:1020)
        at jdk.compiler/com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:396)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$FlowAnalyzer.visitMethodDef(Flow.java:962)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:866)
        at jdk.compiler/com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:396)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$FlowAnalyzer.visitClassDef(Flow.java:925)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:774)
        at jdk.compiler/com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:396)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$FlowAnalyzer.analyzeTree(Flow.java:1325)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$FlowAnalyzer.analyzeTree(Flow.java:1315)
        at jdk.compiler/com.sun.tools.javac.comp.Flow.analyzeTree(Flow.java:216)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.flow(JavaCompiler.java:1393)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.flow(JavaCompiler.java:1367)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:965)
        at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:306)
        at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:165)
        at jdk.compiler/com.sun.tools.javac.Main.compile(Main.java:57)
        at jdk.compiler/com.sun.tools.javac.Main.main(Main.java:43) 

Shubham Kadlag :

It is a reported unresolved bug. The bug is planned to be resolved in jdk 11.

JDK-8203195-Anonymous class type inference results in NPE

Type:                 Bug
Status:               In Progress
Priority:             P2
Resolution:           Unresolved
Affects Version/s:    9, 10, 10.0.1, 11
Fix Version/s:        11
Component/s:          tools
Labels:               dcsfai reproducer-yes webbug 

Subcomponent:         javac
CPU:                  generic   
OS:                   generic

https://bugs.openjdk.java.net/projects/JDK/issues/JDK-8203195?filter=allopenissues

However, there is a work around mentioned in the bug description which states:

Interestingly, changing A.java to do the following:
Object baz => foo.foo(new B<Object>() {});
or changing foo/B.java to the following:

 package foo;

 public class B<T> {

 B(int baz) {   }

 protected B() {   } 
 }

results in a successful compilation.