package io.github.ikysil.javaplayground.narrow;
import java.util.List;
import java.util.Optional;
public class TypeNarrowDemo {
static final class Types {
private Types() throws IllegalAccessException {
throw new IllegalAccessException();
}
static <T> T narrowToNull(final Object obj, final Class<T> expectedType) {
if (expectedType.isInstance(obj)) {
return expectedType.cast(obj);
}
return null;
}
static <T> Optional<T> narrow(final Object obj, final Class<T> expectedType) {
return Optional.ofNullable(obj)
.map(o -> narrowToNull(o, expectedType));
}
}
public static void main(String[] args) {
System.out.println("TypeNarrowDemo Demo");
if (Types.narrowToNull("test", Object.class) != null) {
System.out.println("SUCCESS: String is Object");
}
Types.narrow("test", Object.class)
.ifPresent(o -> System.out.println("SUCCESS: String is Object: " + o));
if (Types.narrowToNull("test", List.class) == null) {
System.out.println("SUCCESS: String is NOT List");
}
Types.narrow("test", List.class)
.ifPresentOrElse(
o -> System.out.println("ERROR: String is NOT List: " + o),
() -> System.out.println("SUCCESS: String is NOT List")
);
}
}
GitHub Repository: java-playground
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