59 lines
1.6 KiB
Java
59 lines
1.6 KiB
Java
// generics/UnboundedWildcards1.java
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// (c)2017 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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import java.util.*;
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public class UnboundedWildcards1 {
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static List list1;
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static List<?> list2;
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static List<? extends Object> list3;
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static void assign1(List list) {
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list1 = list;
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list2 = list;
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//- list3 = list;
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// warning: [unchecked] unchecked conversion
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// list3 = list;
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// ^
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// required: List<? extends Object>
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// found: List
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}
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static void assign2(List<?> list) {
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list1 = list;
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list2 = list;
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list3 = list;
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}
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static void assign3(List<? extends Object> list) {
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list1 = list;
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list2 = list;
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list3 = list;
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}
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public static void main(String[] args) {
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assign1(new ArrayList());
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assign2(new ArrayList());
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//- assign3(new ArrayList());
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// warning: [unchecked] unchecked method invocation:
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// method assign3 in class UnboundedWildcards1
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// is applied to given types
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// assign3(new ArrayList());
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// ^
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// required: List<? extends Object>
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// found: ArrayList
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// warning: [unchecked] unchecked conversion
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// assign3(new ArrayList());
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// ^
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// required: List<? extends Object>
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// found: ArrayList
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// 2 warnings
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assign1(new ArrayList<>());
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assign2(new ArrayList<>());
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assign3(new ArrayList<>());
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// Both forms are acceptable as List<?>:
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List<?> wildList = new ArrayList();
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wildList = new ArrayList<>();
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assign1(wildList);
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assign2(wildList);
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assign3(wildList);
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}
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}
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