Performance: replace toArray(new T[size]) with toArray(new T[0])

Harry Chan · matthiasblaesing · commit 07f3ce053d94 · 2019-01-25T21:34:31.000+01:00
Analysis by Aleksey Shipilёv: https://shipilev.net/blog/2016/arrays-wisdom-ancients/#_conclusin Bottom line: toArray(new T[0]) seems faster, safer, and contractually cleaner, and therefore should be the default choice now. Future VM optimizations may close this performance gap for toArray(new T[size]), rendering the current "believed to be optimal" usages on par with an actually optimal one. Further improvements in toArray APIs would follow the same logic as toArray(new T[0]) — the collection itself should create the appropriate storage.
diff --git a/CHANGES.md b/CHANGES.md
@@ -9,6 +9,7 @@ Features
 --------
 * [#1058](https://github.com/java-native-access/jna/pull/1058): Add selectable timeout to stopService() and improve timeout handling - [@keithharp](https://github.com/keithharp).
 * [#1050](https://github.com/java-native-access/jna/pull/1050): Add `c.s.j.p.win32.VersionHelpers` and supporting functions - [@dbwiddis](https://github.com/dbwiddis).
+* [#1061](https://github.com/java-native-access/jna/pull/1061): replace toArray(new T[size]) with toArray(new T[0]) for better performance - [@hc-codersatlas](https://github.com/hc-codersatlas).
 
 Bug Fixes
 ---------
diff --git a/contrib/platform/src/com/sun/jna/platform/RasterRangesUtils.java b/contrib/platform/src/com/sun/jna/platform/RasterRangesUtils.java
@@ -243,8 +243,8 @@ public static boolean outputOccupiedRanges(int[] pixels, int w, int h, int occup
     private static Set<Rectangle> mergeRects(Set<Rectangle> prev, Set<Rectangle> current) {
         Set<Rectangle> unmerged = new HashSet<Rectangle>(prev);
         if (!prev.isEmpty() && !current.isEmpty()) {
-            Rectangle[] pr = prev.toArray(new Rectangle[prev.size()]);
-            Rectangle[] cr = current.toArray(new Rectangle[current.size()]);
+            Rectangle[] pr = prev.toArray(new Rectangle[0]);
+            Rectangle[] cr = current.toArray(new Rectangle[0]);
             int ipr = 0;
             int icr = 0;
             while (ipr < pr.length && icr < cr.length) {
diff --git a/contrib/platform/src/com/sun/jna/platform/win32/Advapi32Util.java b/contrib/platform/src/com/sun/jna/platform/win32/Advapi32Util.java
@@ -946,7 +946,7 @@ public static String[] registryGetStringArray(HKEY hKey, String value) {
 				result.add(s);
 			}
 		}
-		return result.toArray(new String[result.size()]);
+		return result.toArray(new String[0]);
 	}
 
 	/**
@@ -2632,7 +2632,7 @@ public static ACE_HEADER[] getFileSecurity(String fileName,
                                         result.add(aceStructure);
                                 }
 			}
-			return result.toArray(new ACE_HEADER[result.size()]);
+			return result.toArray(new ACE_HEADER[0]);
 		}
 
                 return aceStructures;
diff --git a/contrib/platform/src/com/sun/jna/platform/win32/DdemlUtil.java b/contrib/platform/src/com/sun/jna/platform/win32/DdemlUtil.java
@@ -1751,7 +1751,7 @@ private Ddeml.HSZPAIR[] onWildconnect(int transactionType, HSZ topic, HSZ servic
             for(WildconnectHandler handler: wildconnectHandler) {
                 hszpairs.addAll(handler.onWildconnect(transactionType, topic, service, convcontext, sameInstance));
             }
-            return hszpairs.toArray(new HSZPAIR[hszpairs.size()]);
+            return hszpairs.toArray(new HSZPAIR[0]);
         }
         
         
diff --git a/contrib/platform/src/com/sun/jna/platform/win32/Kernel32Util.java b/contrib/platform/src/com/sun/jna/platform/win32/Kernel32Util.java
@@ -674,7 +674,7 @@ public static final WinNT.SYSTEM_LOGICAL_PROCESSOR_INFORMATION[] getLogicalProce
         int returnedStructCount = bufferSize.getValue().intValue()
                 / sizePerStruct;
         return (WinNT.SYSTEM_LOGICAL_PROCESSOR_INFORMATION[]) firstInformation
-                .toArray(new WinNT.SYSTEM_LOGICAL_PROCESSOR_INFORMATION[returnedStructCount]);
+                .toArray(new WinNT.SYSTEM_LOGICAL_PROCESSOR_INFORMATION[0]);
     }
 
     /**
diff --git a/contrib/platform/src/com/sun/jna/platform/win32/Netapi32Util.java b/contrib/platform/src/com/sun/jna/platform/win32/Netapi32Util.java
@@ -636,7 +636,7 @@ public static DomainTrust[] getDomainTrusts(String serverName) {
     	}
     	try {
             DS_DOMAIN_TRUSTS domainTrustRefs = new DS_DOMAIN_TRUSTS(domainsPointerRef.getValue());
-            DS_DOMAIN_TRUSTS[] domainTrusts = (DS_DOMAIN_TRUSTS[]) domainTrustRefs.toArray(new DS_DOMAIN_TRUSTS[domainTrustCount.getValue()]);
+            DS_DOMAIN_TRUSTS[] domainTrusts = (DS_DOMAIN_TRUSTS[]) domainTrustRefs.toArray(new DS_DOMAIN_TRUSTS[0]);
             ArrayList<DomainTrust> trusts = new ArrayList<DomainTrust>(domainTrustCount.getValue());
             for(DS_DOMAIN_TRUSTS domainTrust : domainTrusts) {
                 DomainTrust t = new DomainTrust();
diff --git a/contrib/platform/test/com/sun/jna/platform/win32/Netapi32Test.java b/contrib/platform/test/com/sun/jna/platform/win32/Netapi32Test.java
@@ -247,7 +247,7 @@ public void testDsEnumerateDomainTrusts() {
     	assertTrue(domainTrustCount.getValue() >= 0);
 
         DS_DOMAIN_TRUSTS domainTrustRefs = new DS_DOMAIN_TRUSTS(domainsPointerRef.getValue());
-        DS_DOMAIN_TRUSTS[] domainTrusts = (DS_DOMAIN_TRUSTS[]) domainTrustRefs.toArray(new DS_DOMAIN_TRUSTS[domainTrustCount.getValue()]);
+        DS_DOMAIN_TRUSTS[] domainTrusts = (DS_DOMAIN_TRUSTS[]) domainTrustRefs.toArray(new DS_DOMAIN_TRUSTS[0]);
 
     	for(DS_DOMAIN_TRUSTS trust : domainTrusts) {
 			assertTrue(trust.DnsDomainName.length() > 0);
diff --git a/src/com/sun/jna/CallbackReference.java b/src/com/sun/jna/CallbackReference.java
@@ -346,7 +346,7 @@ private static Method getCallbackMethod(Class<?> cls) {
             }
         }
 
-        Method[] methods = pmethods.toArray(new Method[pmethods.size()]);
+        Method[] methods = pmethods.toArray(new Method[0]);
         if (methods.length == 1) {
             return checkMethod(methods[0]);
         }
diff --git a/src/com/sun/jna/NativeLibrary.java b/src/com/sun/jna/NativeLibrary.java
@@ -941,7 +941,7 @@ static double parseVersion(String ver) {
                     }
                     ldPaths.add(0, paths[i]);
                 }
-                paths = ldPaths.toArray(new String[ldPaths.size()]);
+                paths = ldPaths.toArray(new String[0]);
             }
 
             for (int i=0;i < paths.length;i++) {
diff --git a/src/com/sun/jna/Pointer.java b/src/com/sun/jna/Pointer.java
@@ -755,7 +755,7 @@ public Pointer[] getPointerArray(long offset) {
             addOffset += Native.POINTER_SIZE;
             p = getPointer(offset + addOffset);
         }
-        return array.toArray(new Pointer[array.size()]);
+        return array.toArray(new Pointer[0]);
     }
 
     /** Returns an array of {@link Pointer} of the requested size. */
@@ -837,7 +837,7 @@ public String[] getStringArray(long offset, int length, String encoding) {
                 addOffset += Native.POINTER_SIZE;
             }
         }
-        return strings.toArray(new String[strings.size()]);
+        return strings.toArray(new String[0]);
     }
 
     //////////////////////////////////////////////////////////////////////////

Original file line number	Diff line number	Diff line change
`@@ -946,7 +946,7 @@ public static String[] registryGetStringArray(HKEY hKey, String value) {`
`946`	`946`	`result.add(s);`
`947`	`947`	`}`
`948`	`948`	`}`
`949`		`- return result.toArray(new String[result.size()]);`
	`949`	`+ return result.toArray(new String[0]);`
`950`	`950`	`}`
`951`	`951`
`952`	`952`	`/**`
`@@ -2632,7 +2632,7 @@ public static ACE_HEADER[] getFileSecurity(String fileName,`
`2632`	`2632`	`result.add(aceStructure);`
`2633`	`2633`	`}`
`2634`	`2634`	`}`
`2635`		`- return result.toArray(new ACE_HEADER[result.size()]);`
	`2635`	`+ return result.toArray(new ACE_HEADER[0]);`
`2636`	`2636`	`}`
`2637`	`2637`
`2638`	`2638`	`return aceStructures;`
Original file line number	Diff line number	Diff line change
`@@ -1751,7 +1751,7 @@ private Ddeml.HSZPAIR[] onWildconnect(int transactionType, HSZ topic, HSZ servic`
`1751`	`1751`	`for(WildconnectHandler handler: wildconnectHandler) {`
`1752`	`1752`	`hszpairs.addAll(handler.onWildconnect(transactionType, topic, service, convcontext, sameInstance));`
`1753`	`1753`	`}`
`1754`		`- return hszpairs.toArray(new HSZPAIR[hszpairs.size()]);`
	`1754`	`+ return hszpairs.toArray(new HSZPAIR[0]);`
`1755`	`1755`	`}`
`1756`	`1756`
`1757`	`1757`
Original file line number	Diff line number	Diff line change
`@@ -674,7 +674,7 @@ public static final WinNT.SYSTEM_LOGICAL_PROCESSOR_INFORMATION[] getLogicalProce`
`674`	`674`	`int returnedStructCount = bufferSize.getValue().intValue()`
`675`	`675`	`/ sizePerStruct;`
`676`	`676`	`return (WinNT.SYSTEM_LOGICAL_PROCESSOR_INFORMATION[]) firstInformation`
`677`		`- .toArray(new WinNT.SYSTEM_LOGICAL_PROCESSOR_INFORMATION[returnedStructCount]);`
	`677`	`+ .toArray(new WinNT.SYSTEM_LOGICAL_PROCESSOR_INFORMATION[0]);`
`678`	`678`	`}`
`679`	`679`
`680`	`680`	`/**`
Original file line number	Diff line number	Diff line change
`@@ -636,7 +636,7 @@ public static DomainTrust[] getDomainTrusts(String serverName) {`
`636`	`636`	`}`
`637`	`637`	`try {`
`638`	`638`	`DS_DOMAIN_TRUSTS domainTrustRefs = new DS_DOMAIN_TRUSTS(domainsPointerRef.getValue());`
`639`		`- DS_DOMAIN_TRUSTS[] domainTrusts = (DS_DOMAIN_TRUSTS[]) domainTrustRefs.toArray(new DS_DOMAIN_TRUSTS[domainTrustCount.getValue()]);`
	`639`	`+ DS_DOMAIN_TRUSTS[] domainTrusts = (DS_DOMAIN_TRUSTS[]) domainTrustRefs.toArray(new DS_DOMAIN_TRUSTS[0]);`
`640`	`640`	`ArrayList<DomainTrust> trusts = new ArrayList<DomainTrust>(domainTrustCount.getValue());`
`641`	`641`	`for(DS_DOMAIN_TRUSTS domainTrust : domainTrusts) {`
`642`	`642`	`DomainTrust t = new DomainTrust();`
Original file line number	Diff line number	Diff line change
`@@ -346,7 +346,7 @@ private static Method getCallbackMethod(Class<?> cls) {`
`346`	`346`	`}`
`347`	`347`	`}`
`348`	`348`
`349`		`- Method[] methods = pmethods.toArray(new Method[pmethods.size()]);`
	`349`	`+ Method[] methods = pmethods.toArray(new Method[0]);`
`350`	`350`	`if (methods.length == 1) {`
`351`	`351`	`return checkMethod(methods[0]);`
`352`	`352`	`}`
Original file line number	Diff line number	Diff line change
`@@ -941,7 +941,7 @@ static double parseVersion(String ver) {`
`941`	`941`	`}`
`942`	`942`	`ldPaths.add(0, paths[i]);`
`943`	`943`	`}`
`944`		`- paths = ldPaths.toArray(new String[ldPaths.size()]);`
	`944`	`+ paths = ldPaths.toArray(new String[0]);`
`945`	`945`	`}`
`946`	`946`
`947`	`947`	`for (int i=0;i < paths.length;i++) {`
Original file line number	Diff line number	Diff line change
`@@ -755,7 +755,7 @@ public Pointer[] getPointerArray(long offset) {`
`755`	`755`	`addOffset += Native.POINTER_SIZE;`
`756`	`756`	`p = getPointer(offset + addOffset);`
`757`	`757`	`}`
`758`		`- return array.toArray(new Pointer[array.size()]);`
	`758`	`+ return array.toArray(new Pointer[0]);`
`759`	`759`	`}`
`760`	`760`
`761`	`761`	`/** Returns an array of {@link Pointer} of the requested size. */`
`@@ -837,7 +837,7 @@ public String[] getStringArray(long offset, int length, String encoding) {`
`837`	`837`	`addOffset += Native.POINTER_SIZE;`
`838`	`838`	`}`
`839`	`839`	`}`
`840`		`- return strings.toArray(new String[strings.size()]);`
	`840`	`+ return strings.toArray(new String[0]);`
`841`	`841`	`}`
`842`	`842`
`843`	`843`	`//////////////////////////////////////////////////////////////////////////`