Build: Test Java 15 (#157)

* Test under Java 15

* Fix assertion

Author: mincong-h

.github/workflows/main.yml

@@ -20,13 +20,13 @@ jobs:
         key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}
         restore-keys: ${{ runner.os }}-m2
     - run: mvn verify
-  Java-14:
+  Java-15:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
     - uses: actions/setup-java@v1
       with:
-        java-version: 14
+        java-version: 15
     - uses: actions/cache@v1
       with:
         path: ~/.m2

README.md

@@ -6,7 +6,7 @@ in different frameworks. You can run these tests using:
 
     mvn clean install
 
-This project is tested under Java 11 and Java 14.
+This project is tested under Java 11 and Java 15.
 
 ## Module List
 

oca/src/test/java/io/mincong/ocajp/chapter3/ArrayListTest.java

@@ -1,15 +1,8 @@
 package io.mincong.ocajp.chapter3;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertSame;
-import static org.junit.Assert.assertTrue;
-import static org.junit.Assert.fail;
-
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.List;
+import static org.junit.Assert.*;
+
+import java.util.*;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 import org.junit.Test;
@@ -77,12 +70,12 @@ public void testAutoboxing() {
     weights.add(new Double(60)); // ok
 
     weights.add(null);
-    try {
-      double w = weights.get(2); // cannot unwrap
-      fail();
-    } catch (NullPointerException e) {
-      assertNull(e.getMessage());
-    }
+    assertThrows(
+        NullPointerException.class,
+        () -> {
+          @SuppressWarnings("unused")
+          double w = weights.get(2); // cannot unwrap null
+        });
   }
 
   @Test