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Build Identifier: 20100218-1602 Eclipse has only 1 Warning on the given Code, while javac results to 2 Warnings: D:\holger\wba-Performance\JavaPlayGround\src>\holger\jdk1.6.0_21\bin\javac Gener icsWarning.java -Xlint:unchecked GenericsWarning.java:42: warning: [unchecked] unchecked generic array creation o f type java.util.Collection<? extends java.lang.Number>[] for varargs parameter for (Iterator<Number> iter = new IteratorChain<Number>(a, b, c); iter.ha sNext(); ) { ^ GenericsWarning.java:48: warning: [unchecked] unchecked generic array creation o f type java.util.Collection<? extends java.lang.Number>[] for varargs parameter new IteratorChain<Number>(a, b); ^ 2 warnings Reproducible: Always Steps to Reproduce: import java.util.ArrayList; import java.util.Collection; import java.util.Iterator; import java.util.List; public class GenericsWarning { public static class IteratorChain<T> implements Iterator<T> { /** * Minimum of two Collections, eventually more */ public IteratorChain(Collection<? extends T> a, Collection<? extends T> b, Collection<? extends T> ... collections) { // implementation skipped for simplicity } @Override public boolean hasNext() { return false; } @Override public T next() { return null; } @Override public void remove() { throw new UnsupportedOperationException(); } } public static void main(String[] args) { List<Integer> a = new ArrayList<Integer>(); List<Long> b = new ArrayList<Long>(); List<Double> c = new ArrayList<Double>(); // Eclipse and javac both issue a warning for creating an Array of a generic type for (Iterator<Number> iter = new IteratorChain<Number>(a, b, c); iter.hasNext(); ) { Number n = iter.next(); System.out.println(n.intValue()); } // Eclipse does not complain about this, while javac does! new IteratorChain<Number>(a, b); } }
We don't blame the second one, because this is not really using the varargs argument of the constructor. This might be debatable. Srikanth, your call. I don't think this is actually a problem.
Our problem was, that the automatic build (using javac) was set to fail, in case of any warnings. As Eclipse didn't show warnings, we were quite surprised to find the build failed next morning. The first fix was to add a @SuppressWarnings("unchecked") ... but now Eclipse was complaining about the superfluous annotation :-( Actually the varargs parameter won't be null ... therefore it really creates an array of length 0. I've posted this report, as I rate the compatibility with the javac compiler higher. But as you say: It can be seen differently.
(In reply to comment #2) > Actually the varargs parameter won't be null ... therefore it really creates an > array of length 0. Yes, Also see that in the following program we do emit a warning - so to be consistent I'll see what it would take to fix this. import java.util.ArrayList; import java.util.Collection; import java.util.Iterator; import java.util.List; public class GenericsWarning { public static class IteratorChain<T> implements Iterator<T> { public IteratorChain(Collection<? extends T> ... collections) {} public boolean hasNext() { return false; } public T next() { return null; } public void remove() { throw new UnsupportedOperationException(); } public static void main(String[] args) { List<Integer> a = new ArrayList<Integer>(); List<Long> b = new ArrayList<Long>(); List<Double> c = new ArrayList<Double>(); for (Iterator<Number> iter = new IteratorChain<Number>(); iter.hasNext(); ) { Number n = iter.next(); System.out.println(n.intValue()); } } } }
Created attachment 188982 [details] Patch under test This patch makes eclipse behavior self consistent as well as consistent with javac.
Passes all tests, Ayush, please review, TIA
Released in HEAD for 3.7 M6
Verified for 3.7M6 using build I20110301-1537.
