Java Reference
In-Depth Information
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// Fig. 20.14: WildcardTest.java
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// Wildcard test program.
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import
java.util.ArrayList;
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public class
WildcardTest
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{
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public static void
main(String[] args)
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{
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// create, initialize and output ArrayList of Integers, then
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// display total of the elements
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Integer[] integers = {
1
,
2
,
3
,
4
,
5
};
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ArrayList<Integer> integerList =
new
ArrayList<>();
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// insert elements in integerList
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for
(Integer element : integers)
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integerList.add(element);
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System.out.printf(
"integerList contains: %s%n"
, integerList);
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System.out.printf(
"Total of the elements in integerList: %.0f%n%n"
,
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sum(integerList)
);
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// create, initialize and output ArrayList of Doubles, then
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// display total of the elements
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Double[] doubles = {
1.1
,
3.3
,
5.5
};
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ArrayList<Double> doubleList =
new
ArrayList<>();
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// insert elements in doubleList
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for
(Double element : doubles)
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doubleList.add(element);
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System.out.printf(
"doubleList contains: %s%n"
, doubleList);
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System.out.printf(
"Total of the elements in doubleList: %.1f%n%n"
,
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sum(doubleList)
);
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// create, initialize and output ArrayList of Numbers containing
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// both Integers and Doubles, then display total of the elements
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Number[] numbers = {
1
,
2.4
,
3
,
4.1
};
// Integers and Doubles
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ArrayList<Number> numberList =
new
ArrayList<>();
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// insert elements in numberList
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for
(Number element : numbers)
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numberList.add(element);
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System.out.printf(
"numberList contains: %s%n"
, numberList);
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System.out.printf(
"Total of the elements in numberList: %.1f%n"
,
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sum(numberList)
);
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}
// end main
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// total the elements; using a wildcard in the ArrayList parameter
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public static double
sum(
ArrayList<?
extends
Number>
list)
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{
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double
total =
0
;
// initialize total
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Fig. 20.14
|
Wildcard test program. (Part 1 of 2.)
