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

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.

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
 ---------

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) {

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;

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]);
         }
 
 

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]);
     }
 
     /**

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();

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);

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]);
         }

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++) {

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]);
     }
 
     //////////////////////////////////////////////////////////////////////////