how to write a generic method in java code example
Example 1: java generic type method
// generic methods
public <T> List<T> fromArrayToList(T[] a) {
return Arrays.stream(a).collect(Collectors.toList());
}
public static <T, G> List<G> fromArrayToList(T[] a, Function<T, G> mapperFunction) {
return Arrays.stream(a)
.map(mapperFunction)
.collect(Collectors.toList());
}
// bounded generics
public <T extends Number> List<T> fromArrayToList(T[] a) {
...
}
//multiple bounds
<T extends Number & Comparable>
// upper bound wildcards
public static void paintAllBuildings(List<? extends Building> buildings) {
...
}
// lower bound wildcard
<? super T>
Example 2: generic argument java
static void fromArrayToCollection(Object[] a, Collection<?> c) {
for (Object o : a) {
c.add(o); // compile-time error
}
}