From 4dba865995e4940f897c18afff60501fa9cce05a Mon Sep 17 00:00:00 2001
From: Harry Chan <38070640+hc-codersatlas@users.noreply.github.com>
Date: Tue, 29 Jan 2019 13:42:02 +1100
Subject: [PATCH] Optimize toArray (#484)

replace toArray(new T[size]) with toArray(new T[0]) for better performance

https://shipilev.net/blog/2016/arrays-wisdom-ancients/#_conclusion
---
 .../taobao/arthas/core/command/monitor200/ThreadCommand.java    | 2 +-
 .../main/java/com/taobao/arthas/core/config/FeatureCodec.java   | 2 +-
 core/src/main/java/com/taobao/arthas/core/util/StringUtils.java | 2 +-
 .../main/java/com/taobao/arthas/core/util/TypeRenderUtils.java  | 2 +-
 .../java/com/taobao/arthas/core/util/reflect/FieldUtils.java    | 2 +-
 5 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/core/src/main/java/com/taobao/arthas/core/command/monitor200/ThreadCommand.java b/core/src/main/java/com/taobao/arthas/core/command/monitor200/ThreadCommand.java
index aa4c76692..11ca228ae 100644
--- a/core/src/main/java/com/taobao/arthas/core/command/monitor200/ThreadCommand.java
+++ b/core/src/main/java/com/taobao/arthas/core/command/monitor200/ThreadCommand.java
@@ -129,7 +129,7 @@ public class ThreadCommand extends AnnotatedCommand {
 
     private void processTopBusyThreads(CommandProcess process) {
         Map<Long, Long> topNThreads = ThreadUtil.getTopNThreads(sampleInterval, topNBusy);
-        Long[] tids = topNThreads.keySet().toArray(new Long[topNThreads.keySet().size()]);
+        Long[] tids = topNThreads.keySet().toArray(new Long[0]);
         ThreadInfo[] threadInfos = threadMXBean.getThreadInfo(ArrayUtils.toPrimitive(tids), true, true);
         if (threadInfos == null) {
             process.write("thread do not exist! id: " + id + "\n");
diff --git a/core/src/main/java/com/taobao/arthas/core/config/FeatureCodec.java b/core/src/main/java/com/taobao/arthas/core/config/FeatureCodec.java
index 250dff9f7..fa9c2e354 100644
--- a/core/src/main/java/com/taobao/arthas/core/config/FeatureCodec.java
+++ b/core/src/main/java/com/taobao/arthas/core/config/FeatureCodec.java
@@ -236,7 +236,7 @@ public class FeatureCodec {
 
         }
 
-        return segmentArrayList.toArray(new String[segmentArrayList.size()]);
+        return segmentArrayList.toArray(new String[0]);
     }
 
 
diff --git a/core/src/main/java/com/taobao/arthas/core/util/StringUtils.java b/core/src/main/java/com/taobao/arthas/core/util/StringUtils.java
index 79a96f0c9..9774e41f8 100644
--- a/core/src/main/java/com/taobao/arthas/core/util/StringUtils.java
+++ b/core/src/main/java/com/taobao/arthas/core/util/StringUtils.java
@@ -538,7 +538,7 @@ public abstract class StringUtils {
 
 
     public static String[] toStringArray(Collection<String> collection) {
-        return collection == null?null:(String[])collection.toArray(new String[collection.size()]);
+        return collection == null?null:(String[])collection.toArray(new String[0]);
     }
 
     public static String[] split(String toSplit, String delimiter) {
diff --git a/core/src/main/java/com/taobao/arthas/core/util/TypeRenderUtils.java b/core/src/main/java/com/taobao/arthas/core/util/TypeRenderUtils.java
index 430ae5c56..27669e011 100644
--- a/core/src/main/java/com/taobao/arthas/core/util/TypeRenderUtils.java
+++ b/core/src/main/java/com/taobao/arthas/core/util/TypeRenderUtils.java
@@ -160,6 +160,6 @@ public class TypeRenderUtils {
                 types.add(annotation.annotationType());
             }
         }
-        return StringUtils.concat(",", types.toArray(new Class<?>[types.size()]));
+        return StringUtils.concat(",", types.toArray(new Class<?>[0]));
     }
 }
diff --git a/core/src/main/java/com/taobao/arthas/core/util/reflect/FieldUtils.java b/core/src/main/java/com/taobao/arthas/core/util/reflect/FieldUtils.java
index 932cdc43f..9aa3fd13a 100644
--- a/core/src/main/java/com/taobao/arthas/core/util/reflect/FieldUtils.java
+++ b/core/src/main/java/com/taobao/arthas/core/util/reflect/FieldUtils.java
@@ -238,7 +238,7 @@ public class FieldUtils {
      */
     public static Field[] getAllFields(final Class<?> cls) {
         final List<Field> allFieldsList = getAllFieldsList(cls);
-        return allFieldsList.toArray(new Field[allFieldsList.size()]);
+        return allFieldsList.toArray(new Field[0]);
     }
 
     /**