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Test your Java generics knowledge with this pop quiz: which are the valid statements?
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| import java.util.List; | |
| public class GenericsQuiz { | |
| List<Number> listOfNumber; | |
| List<? extends Number> listOfExtendsNumber; | |
| List<? super Number> listOfSuperNumber; | |
| List<Integer> listOfInteger; | |
| List<? extends Integer> listOfExtendsInteger; | |
| List<? super Integer> listOfSuperInteger; | |
| Integer integer; | |
| Number number; | |
| public void assign() { | |
| listOfNumber = listOfExtendsNumber; | |
| listOfNumber = listOfSuperNumber; | |
| listOfNumber = listOfInteger; | |
| listOfNumber = listOfExtendsInteger; | |
| listOfNumber = listOfSuperInteger; | |
| listOfExtendsNumber = listOfNumber; | |
| listOfExtendsNumber = listOfSuperNumber; | |
| listOfExtendsNumber = listOfInteger; | |
| listOfExtendsNumber = listOfExtendsInteger; | |
| listOfExtendsNumber = listOfSuperInteger; | |
| listOfSuperNumber = listOfNumber; | |
| listOfSuperNumber = listOfExtendsNumber; | |
| listOfSuperNumber = listOfInteger; | |
| listOfSuperNumber = listOfExtendsInteger; | |
| listOfSuperNumber = listOfSuperInteger; | |
| listOfInteger = listOfNumber; | |
| listOfInteger = listOfExtendsNumber; | |
| listOfInteger = listOfSuperNumber; | |
| listOfInteger = listOfExtendsInteger; | |
| listOfInteger = listOfSuperInteger; | |
| listOfExtendsInteger = listOfNumber; | |
| listOfExtendsInteger = listOfExtendsNumber; | |
| listOfExtendsInteger = listOfSuperNumber; | |
| listOfExtendsInteger = listOfInteger; | |
| listOfExtendsInteger = listOfSuperInteger; | |
| listOfSuperInteger = listOfNumber; | |
| listOfSuperInteger = listOfExtendsNumber; | |
| listOfSuperInteger = listOfSuperNumber; | |
| listOfSuperInteger = listOfInteger; | |
| listOfSuperInteger = listOfExtendsInteger; | |
| } | |
| public void add() { | |
| listOfNumber.add(integer); | |
| listOfNumber.add(number); | |
| listOfExtendsNumber.add(integer); | |
| listOfExtendsNumber.add(number); | |
| listOfSuperNumber.add(integer); | |
| listOfSuperNumber.add(number); | |
| listOfInteger.add(integer); | |
| listOfInteger.add(number); | |
| listOfExtendsInteger.add(integer); | |
| listOfExtendsInteger.add(number); | |
| listOfSuperInteger.add(integer); | |
| listOfSuperInteger.add(number); | |
| } | |
| public void get() { | |
| number = listOfNumber.get(0); | |
| number = listOfExtendsNumber.get(0); | |
| number = listOfSuperNumber.get(0); | |
| number = listOfInteger.get(0); | |
| number = listOfExtendsInteger.get(0); | |
| number = listOfSuperInteger.get(0); | |
| integer = listOfNumber.get(0); | |
| integer = listOfExtendsNumber.get(0); | |
| integer = listOfSuperNumber.get(0); | |
| integer = listOfInteger.get(0); | |
| integer = listOfExtendsInteger.get(0); | |
| integer = listOfSuperInteger.get(0); | |
| } | |
| } |
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