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UnboundedWildcards1.java
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// generics/UnboundedWildcards1.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
import java.util.*;
public class UnboundedWildcards1 {
static List list1;
static List<?> list2;
static List<? extends Object> list3;
static void assign1(List list) {
list1 = list;
list2 = list;
//- list3 = list;
// warning: [unchecked] unchecked conversion
// list3 = list;
// ^
// required: List<? extends Object>
// found: List
}
static void assign2(List<?> list) {
list1 = list;
list2 = list;
list3 = list;
}
static void assign3(List<? extends Object> list) {
list1 = list;
list2 = list;
list3 = list;
}
public static void main(String[] args) {
assign1(new ArrayList());
assign2(new ArrayList());
//- assign3(new ArrayList());
// warning: [unchecked] unchecked method invocation:
// method assign3 in class UnboundedWildcards1
// is applied to given types
// assign3(new ArrayList());
// ^
// required: List<? extends Object>
// found: ArrayList
// warning: [unchecked] unchecked conversion
// assign3(new ArrayList());
// ^
// required: List<? extends Object>
// found: ArrayList
// 2 warnings
assign1(new ArrayList<>());
assign2(new ArrayList<>());
assign3(new ArrayList<>());
// Both forms are acceptable as List<?>:
List<?> wildList = new ArrayList();
wildList = new ArrayList<>();
assign1(wildList);
assign2(wildList);
assign3(wildList);
}
}