gs gs128 Java Generics - Java Restrictions on Generics - Quiz No.1

 public class BoxDemo { public static <U> void addBox(U u, java.util.List<Box<U>> boxes) { Box<U> box = new Box<>(); box.set(u); boxes.add(box); } public static <U> void outputBoxes(java.util.List<Box<U>> boxes) { int counter = 0; for (Box<U> box: boxes) { U boxContents = box.get(); System.out.println("Box #" + counter + " contains [" + boxContents.toString() + "]"); counter++; } } public static void main(String[] args) { java.util.ArrayList<Box<Integer>> listOfIntegerBoxes = new java.util.ArrayList<>(); BoxDemo.<Integer>addBox(Integer.valueOf(10), listOfIntegerBoxes); BoxDemo.outputBoxes(listOfIntegerBoxes); } }

 import java.util.*; public class genericstack <E> { Stack <E> stk = new Stack <E>(); public void push(E obj) { stk.push(obj); } public E pop() { E obj = stk.pop(); return obj; } } class Output { public static void main(String args[]) { genericstack <String> gs = new genericstack<String>(); gs.push("Hello"); System.out.print(gs.pop() + " "); genericstack <Integer> gs = new genericstack<Integer>(); gs.push(36); System.out.println(gs.pop()); } }

 import java.util.*; class Output { public static double sumOfList(List<? extends Number> list) { double s = 0.0; for (Number n : list) s += n.doubleValue(); return s; } public static void main(String args[]) { List<Double> ld = Arrays.asList(1.2, 2.3, 3.5); System.out.println(sumOfList(ld)); } }

 import java.util.*; class Output { public static void addNumbers(List<? super Integer> list) { for (int i = 1; i <= 10; i++) { list.add(i); } } public static void main(String args[]) { List<Double> ld = Arrays.asList(); addnumbers(10.4); System.out.println("getList(2)"); } }

 import java.util.*; public class genericstack <E> { Stack <E> stk = new Stack <E>(); public void push(E obj) { stk.push(obj); } public E pop() { E obj = stk.pop(); return obj; } } class Output { public static void main(String args[]) { genericstack <Integer> gs = new genericstack<Integer>(); gs.push(36); System.out.println(gs.pop()); } }