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August 29, 2015 13:57
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Exploring wildcard types, or the so called question mark type, in Java.
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| public void process3(java.util.List<?>); | |
| Code: | |
| 0: aload_1 | |
| 1: invokeinterface #2, 1 // InterfaceMethod java/util/List.iterator:()Ljava/util/Iterator; | |
| 6: astore_2 | |
| 7: aload_2 | |
| 8: invokeinterface #3, 1 // InterfaceMethod java/util/Iterator.hasNext:()Z | |
| 13: ifeq 31 | |
| 16: aload_2 | |
| 17: invokeinterface #4, 1 // InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object; | |
| 22: astore_3 | |
| 23: aload_3 | |
| 24: invokevirtual #5 // Method java/lang/Object.toString:()Ljava/lang/String; | |
| 27: pop | |
| 28: goto 7 | |
| 31: return |
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| package wild; | |
| import java.util.ArrayList; | |
| import java.util.Arrays; | |
| import java.util.List; | |
| public class Viewer { | |
| public void process1(List<Object> items) { | |
| for (Object i : items) | |
| i.toString(); | |
| } | |
| public void process2(List<Item> items) { | |
| for (Item i : items) | |
| i.process(); | |
| } | |
| public void process3(List<?> items) { | |
| for (Object i : items) | |
| i.toString(); | |
| } | |
| public void process4(List<? extends Item> items) { | |
| for (Item i : items) | |
| i.process(); | |
| } | |
| public static void main(String[] args) { | |
| Viewer viewer = new Viewer(); | |
| viewer.process3(new ArrayList<TwitterItem>(Arrays.asList(new TwitterItem() { | |
| @Override | |
| public void process() { | |
| // some computation | |
| } | |
| @Override | |
| public String toString() { | |
| return "twitteritem"; | |
| } | |
| }))); | |
| } | |
| } |
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