OptionalBasicExample.java
package com.mkyong;
import java.util.Optional;
public class OptionalBasicExample {
public static void main(String[] args) {
Optional<String> gender = Optional.of("MALE");
String answer1 = "Yes";
String answer2 = null;
System.out.println("Non-Empty Optional:" + gender);
System.out.println("Non-Empty Optional: Gender value : " + gender.get());
System.out.println("Empty Optional: " + Optional.empty());
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));
}
}
Output
Non-Empty Optional:Optional[MALE]
Non-Empty Optional: Gender value : MALE
Empty Optional: Optional.empty
ofNullable on Non-Empty Optional: Optional[Yes]
ofNullable on Empty Optional: Optional.empty
Exception in thread "main" java.lang.NullPointerException
at java.util.Objects.requireNonNull(Objects.java:203)
at java.util.Optional.<init>(Optional.java:96)
at java.util.Optional.of(Optional.java:108)
//...
2. Optional.map and flatMap
OptionalMapFlapMapExample.java
package com.mkyong;
import java.util.Optional;
public class OptionalMapFlapMapExample {
public static void main(String[] args) {
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(gender -> gender.map(String::toUpperCase)));
System.out.println("Optional.flatMap :: " + nonEmptyOtionalGender.flatMap(gender -> gender.map(String::toUpperCase)));
}
}
Output
Non-Empty Optional:: Optional[MALE]
Empty Optional :: Optional.empty
Optional value :: Optional[Optional[male]]
Optional.map :: Optional[Optional[MALE]]
Optional.flatMap :: Optional[MALE]3. Optional.filter
OptionalFilterExample.java
package com.mkyong;
import java.util.Optional;
public class OptionalFilterExample {
public static void main(String[] args) {
Optional<String> gender = Optional.of("MALE");
Optional<String> emptyGender = Optional.empty();
//Filter on Optional
System.out.println(gender.filter(g -> g.equals("male"))); //Optional.empty
System.out.println(gender.filter(g -> g.equalsIgnoreCase("MALE"))); //Optional[MALE]
System.out.println(emptyGender.filter(g -> g.equalsIgnoreCase("MALE"))); //Optional.empty
}
}
Output
Optional.empty
Optional[MALE]
Optional.empty4. Optional isPresent and ifPresent
Optional.isPresent() returns true if the given Optional object is non-empty. Otherwise it returns false.
Optional.ifPresent() performs given action if the given Optional object is non-empty. Otherwise it returns false.
OptionalIfPresentExample.java
package com.mkyong;
import java.util.Optional;
public class OptionalIfPresentExample {
public static void main(String[] args) {
Optional<String> gender = Optional.of("MALE");
Optional<String> emptyGender = Optional.empty();
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."));
}
}
Output
Value available.
In gender Option, value available.
5. Optional orElse methods
It returns the value if present in Optional Container. Otherwise returns given default value.
OptionalOrElseExample.java
package com.mkyong;
import java.util.Optional;
public class OptionalOrElseExample {
public static void main(String[] args) {
Optional<String> gender = Optional.of("MALE");
Optional<String> emptyGender = Optional.empty();
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>
}
}
Output
MALE
<N/A>
MALE
<N/A>
6. Without Java 8 Optional
As everyone is familiar with Online Shopping. Let us assume that we want to implement a Mobile Product Module for a famous e-Commerce website.
Let us implement Mobile Domain module Without Java 8 Optional.
ScreenResolution.java
package com.mkyong.without.optional;
public class ScreenResolution {
private int width;
private int height;
public ScreenResolution(int width, int height){
this.width = width;
this.height = height;
}
public int getWidth() {
return width;
}
public int getHeight() {
return height;
}
}
DisplayFeatures.java
package com.mkyong.without.optional;
public class DisplayFeatures {
private String size; // In inches
private ScreenResolution resolution;
public DisplayFeatures(String size, ScreenResolution resolution){
this.size = size;
this.resolution = resolution;
}
public String getSize() {
return size;
}
public ScreenResolution getResolution() {
return resolution;
}
}
Mobile.java
package com.mkyong.without.optional;
public class Mobile {
private long id;
private String brand;
private String name;
private DisplayFeatures displayFeatures;
// Likewise we can see Memory Features, Camera Features etc.
public Mobile(long id, String brand, String name,
DisplayFeatures displayFeatures){
this.id = id;
this.brand = brand;
this.name = name;
this.displayFeatures = displayFeatures;
}
public long getId() {
return id;
}
public String getBrand() {
return brand;
}
public String getName() {
return name;
}
public DisplayFeatures getDisplayFeatures() {
return displayFeatures;
}
}
Here if we observe getMobileScreenWidth() method, it has lot of boiler plate code with lots null checks. Before Java 8, we should do all these non-sense stuff to avoid Runtime NullPointerExceptions.
MobileService.java
package com.mkyong.without.optional;
public class MobileService {
public int getMobileScreenWidth(Mobile mobile){
if(mobile != null){
DisplayFeatures dfeatures = mobile.getDisplayFeatures();
if(dfeatures != null){
ScreenResolution resolution = dfeatures.getResolution();
if(resolution != null){
return resolution.getWidth();
}
}
}
return 0;
}
}
Develop one test application to test these Domain objects.
MobileTesterWithoutOptional.java
package com.mkyong.without.optional;
public class MobileTesterWithoutOptional {
public static void main(String[] args) {
ScreenResolution resolution = new ScreenResolution(750,1334);
DisplayFeatures dfeatures = new DisplayFeatures("4.7", resolution);
Mobile mobile = new Mobile(2015001, "Apple", "iPhone 6s", dfeatures);
MobileService mService = new MobileService();
int mobileWidth = mService.getMobileScreenWidth(mobile);
System.out.println("Apple iPhone 6s Screen Width = " + mobileWidth);
ScreenResolution resolution2 = new ScreenResolution(0,0);
DisplayFeatures dfeatures2 = new DisplayFeatures("0", resolution2);
Mobile mobile2 = new Mobile(2015001, "Apple", "iPhone 6s", dfeatures2);
int mobileWidth2 = mService.getMobileScreenWidth(mobile2);
System.out.println("Apple iPhone 16s Screen Width = " + mobileWidth2);
}
}
Output
Apple iPhone 6s Screen Width = 750
Apple iPhone 16s Screen Width = 0
7. With Java 8 Optional
Now develop same domain models using Java 8 Optional construct with clean and neat way.
P.S ScreenResolution.java no change. Please refer above section.
DisplayFeatures.java
package com.mkyong.with.optional;
import java.util.Optional;
public class DisplayFeatures {
private String size; // In inches
private Optional<ScreenResolution> resolution;
public DisplayFeatures(String size, Optional<ScreenResolution> resolution){
this.size = size;
this.resolution = resolution;
}
public String getSize() {
return size;
}
public Optional<ScreenResolution> getResolution() {
return resolution;
}
}
Mobile.java
package com.mkyong.with.optional;
import java.util.Optional;
public class Mobile {
private long id;
private String brand;
private String name;
private Optional<DisplayFeatures> displayFeatures;
// Like wise we can see MemoryFeatures, CameraFeatures etc.
// For simplicity, using only one Features
public Mobile(long id, String brand, String name, Optional<DisplayFeatures> displayFeatures){
this.id = id;
this.brand = brand;
this.name = name;
this.displayFeatures = displayFeatures;
}
public long getId() {
return id;
}
public String getBrand() {
return brand;
}
public String getName() {
return name;
}
public Optional<DisplayFeatures> getDisplayFeatures() {
return displayFeatures;
}
}
Here we can observe that how clean our getMobileScreenWidth() API without null checks and boiler plate code. We don not worry about NullPointerExceptions at run-time.
MobileService.java
package com.mkyong.with.optional;
import java.util.Optional;
public class MobileService {
public Integer getMobileScreenWidth(Optional<Mobile> mobile){
return mobile.flatMap(Mobile::getDisplayFeatures)
.flatMap(DisplayFeatures::getResolution)
.map(ScreenResolution::getWidth)
.orElse(0);
}
}
Now develop one test component
MobileTesterWithOptional.java
package com.mkyong.with.optional;
import java.util.Optional;
public class MobileTesterWithOptional {
public static void main(String[] args) {
ScreenResolution resolution = new ScreenResolution(750,1334);
DisplayFeatures dfeatures = new DisplayFeatures("4.7", Optional.of(resolution));
Mobile mobile = new Mobile(2015001, "Apple", "iPhone 6s", Optional.of(dfeatures));
MobileService mService = new MobileService();
int width = mService.getMobileScreenWidth(Optional.of(mobile));
System.out.println("Apple iPhone 6s Screen Width = " + width);
Mobile mobile2 = new Mobile(2015001, "Apple", "iPhone 6s", Optional.empty());
int width2 = mService.getMobileScreenWidth(Optional.of(mobile2));
System.out.println("Apple iPhone 16s Screen Width = " + width2);
}
}
Output
Apple iPhone 6s Screen Width = 750
Apple iPhone 16s Screen Width = 0
8. Where does Java Optional fits?
If we observe above real-time Retail Domain use-case, we should know that Java Optional construct is useful at the following places.
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>> { }
from http://www.mkyong.com/java8/java-8-optional-in-depth/