Assign IonSystemBuilder sub-builder defaults in the constructor

src/jmh/java/com/amazon/ion/IonSystemBuilderCopyBenchmark.java

@@ -0,0 +1,45 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+package com.amazon.ion;
+
+import com.amazon.ion.system.IonSystemBuilder;
+import com.amazon.ion.system.SimpleCatalog;
+import java.util.concurrent.TimeUnit;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+
+/**
+ * Measures the cost of copying an {@link IonSystemBuilder}.
+ */
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@Fork(value = 1)
+@Warmup(iterations = 3, time = 1, timeUnit = TimeUnit.SECONDS)
+@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
+@State(Scope.Benchmark)
+public class IonSystemBuilderCopyBenchmark {
+
+    private final IonCatalog catalog = new SimpleCatalog();
+
+    @Benchmark
+    public IonSystemBuilder copy() {
+        return IonSystemBuilder.standard().copy();
+    }
+
+    @Benchmark
+    public IonSystemBuilder withCatalog() {
+        return IonSystemBuilder.standard().withCatalog(catalog);
+    }
+
+    @Benchmark
+    public IonSystem buildWithCatalog() {
+        return IonSystemBuilder.standard().withCatalog(catalog).build();
+    }
+}

src/main/java/com/amazon/ion/system/IonSystemBuilder.java

@@ -91,15 +91,25 @@ public static IonSystemBuilder standard()
     IonCatalog myCatalog;
     boolean myStreamCopyOptimized = false;
 
-    IonTextWriterBuilder textWriterBuilder = IonTextWriterBuilder.standard().withCharsetAscii();
-    IonBinaryWriterBuilder binaryWriterBuilder = IonBinaryWriterBuilder.standard();
-    IonReaderBuilder readerBuilder = IonReaderBuilder.standard();
+    // These are deliberately declared without initializers; their defaults are
+    // assigned by the no-argument constructor. See the note there.
+    IonTextWriterBuilder textWriterBuilder;
+    IonBinaryWriterBuilder binaryWriterBuilder;
+    IonReaderBuilder readerBuilder;
 
 
     /** You no touchy. */
     private IonSystemBuilder()
     {
-        // empty
+        // The defaults are assigned here rather than in field initializers
+        // because Java runs field initializers as part of *every* constructor,
+        // including the copy constructor below, whose body then overwrites all
+        // three fields. That made copy() -- and therefore mutable(),
+        // immutable(), and every withXxx() -- allocate a full set of default
+        // writer/reader builders only to immediately discard them.
+        textWriterBuilder = IonTextWriterBuilder.standard().withCharsetAscii();
+        binaryWriterBuilder = IonBinaryWriterBuilder.standard();
+        readerBuilder = IonReaderBuilder.standard();
     }
 
     private IonSystemBuilder(IonSystemBuilder that)

src/test/java/com/amazon/ion/system/IonSystemBuilderTest.java

@@ -1,23 +1,10 @@
-/*
- * Copyright 2007-2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License").
- * You may not use this file except in compliance with the License.
- * A copy of the License is located at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * or in the "license" file accompanying this file. This file is distributed
- * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
- * express or implied. See the License for the specific language governing
- * permissions and limitations under the License.
- */
-
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
 package com.amazon.ion.system;
 
 import static com.amazon.ion.impl.lite._Private_LiteDomTrampoline.isLiteSystem;
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNotSame;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
@@ -201,5 +188,30 @@ public void testCopy()
         assertNotSame(b1, b2);
         assertSame(b1.getCatalog(),     b2.getCatalog());
         assertSame(b1.isStreamCopyOptimized(), b2.isStreamCopyOptimized());
+        assertSame(b1.getIonTextWriterBuilder(),   b2.getIonTextWriterBuilder());
+        assertSame(b1.getIonBinaryWriterBuilder(), b2.getIonBinaryWriterBuilder());
+        assertSame(b1.getReaderBuilder(),          b2.getReaderBuilder());
+    }
+
+    @Test
+    public void testStandardHasDefaultSubBuilders()
+    {
+        IonSystemBuilder b = IonSystemBuilder.standard();
+        assertNotNull(b.getIonTextWriterBuilder());
+        assertNotNull(b.getIonBinaryWriterBuilder());
+        assertNotNull(b.getReaderBuilder());
+        assertSame(IonTextWriterBuilder.ASCII, b.getIonTextWriterBuilder().getCharset());
+    }
+
+    @Test
+    public void testCopyCarriesTheSameDefaultSubBuilders()
+    {
+        IonSystemBuilder standard = IonSystemBuilder.standard();
+        IonSystemBuilder copy = standard.copy().mutable().copy().immutable().mutable();
+        assertNotSame(standard, copy);
+        assertSame(standard.getIonTextWriterBuilder(),   copy.getIonTextWriterBuilder());
+        assertSame(standard.getIonBinaryWriterBuilder(), copy.getIonBinaryWriterBuilder());
+        assertSame(standard.getReaderBuilder(),          copy.getReaderBuilder());
+        assertSame(IonTextWriterBuilder.ASCII, copy.getIonTextWriterBuilder().getCharset());
     }
 }