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package java8;
import java.util.Optional;
public class OptionalTest {
public static void main(String[] args) {
//Basic
Optional<String> gender = Optional.of("MALE");
System.out.println("Non-Empty Optional:" + gender);
System.out.println("Non-Empty Optional: Gender value : " + gender.get());
System.out.println("Empty Optional: " + Optional.empty());
String answer1 = "Yes";
String answer2 = null;
System.out.println("ofNullable on Non-Empty Optional: " + Optional.ofNullable(answer1));
System.out.println("ofNullable on Empty Optional: " + Optional.ofNullable(answer2));
// java.lang.NullPointerException
//System.out.println("ofNullable on Non-Empty Optional: " + Optional.of(answer2));
//Optional.map and flatMap
Optional<String> nonEmptyGender = Optional.of("male");
Optional<String> emptyGender = Optional.empty();
System.out.println("Non-Empty Optional:: " + nonEmptyGender.map(String::toUpperCase));
System.out.println("Empty Optional :: " + emptyGender.map(String::toUpperCase));
Optional<Optional<String>> nonEmptyOtionalGender = Optional.of(Optional.of("male"));
System.out.println("Optional value :: " + nonEmptyOtionalGender);
System.out.println("Optional.map :: " + nonEmptyOtionalGender.map(g -> g.map(String::toUpperCase)));
System.out.println("Optional.flatMap :: " + nonEmptyOtionalGender.flatMap(g -> g.map(String::toUpperCase)));
//Filter on Optional
System.out.println(gender.filter(g -> g.equals("male"))); //Optional.empty
System.out.println(gender.filter(g -> g.equals("MALE"))); //Optional[MALE]
System.out.println(emptyGender.filter(g -> g.equals("MALE"))); //Optional.empty
//Optional isPresent and ifPresent
if (gender.isPresent()) {
System.out.println("Value available.");
} else {
System.out.println("Value not available.");
}
gender.ifPresent(g -> System.out.println("In gender Option, value available."));
//condition failed, no output print
emptyGender.ifPresent(g -> System.out.println("In emptyGender Option, value available."));
//Optional orElse methods
System.out.println(gender.orElse("<N/A>")); //MALE
System.out.println(emptyGender.orElse("<N/A>")); //<N/A>
System.out.println(gender.orElseGet(() -> "<N/A>")); //MALE
System.out.println(emptyGender.orElseGet(() -> "<N/A>")); //<N/A>
//Where does Java Optional fits?
/*
* 8.1 Method Parameter
public void setResolution(Optional<ScreenResolution> resolution) {
this.resolution = resolution;
}
8.2 Method Return Type
public Optional<ScreenResolution> getResolution() {
return resolution;
}
8.3 Constructor Parameter
public DisplayFeatures(String size, Optional<ScreenResolution> resolution){
this.size = size;
this.resolution = resolution;
}
8.4 Variable Declaration
private Optional<ScreenResolution> resolution;
8.5 Class Level
public class B
public class A<T extends Optional<B>> { }
*/
}
}