CODEWITHSUNDEEP
javagenericswildcard
Adithya
Adithya

Reputation: 2975

Lower bounded wildcards in java

Consider the following example,

List<? super Number> list1 = new ArrayList<>();
list1.add(10);
list1.add(10.10);
list1.add(20.20d);

and another list to which i assign list1

List<? super Integer> list = list1;
System.out.println(list.toString());

Now, when i print the list it contains double values also BUT the list is only supposed to hold Integer and anything above Integer.

If the above is fine then shouldn't the following compile as well ?

list.add(30.30);

Upvotes: 1

Views: 171

Answers (1)

Louis Wasserman
Louis Wasserman

Reputation: 198014

Everything makes sense if you consider the possible things you could assign to it.

List<? super Number> list1 = new ArrayList<Object>(); // works
List<? super Number> list1 = new ArrayList<Number>(); // works
List<? super Number> list1 = new ArrayList<Integer>(); // doesn't work

Anything that works on the right hand side will accept a Double.

List<? super Integer> list = new ArrayList<Object>(); // works
List<? super Integer> list = new ArrayList<Number>(); // works
List<? super Integer> list = new ArrayList<Integer>(); // works

Anything that you could assign to list1 you could also assign to list. So list = list1 works just fine. But not all of the things you could assign to list will accept a Double, so it doesn't compile.

Upvotes: 5

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