Java 8 Optional In Depth

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));

    }

}

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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)));

    }

}

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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

    }

}

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Output

Optional.empty
Optional[MALE]
Optional.empty

4. 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."));

    }

}

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Output

Value available.
In gender Option, value available.

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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>

    }

}

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Output

MALE
<N/A>
MALE
<N/A>

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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;
	}

}

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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;
	}

}

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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;
	}

}

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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;

	}

}

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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);

	}

}

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Output

Apple iPhone 6s Screen Width = 750
Apple iPhone 16s Screen Width = 0

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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;
	}

}

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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;
	}

}

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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);

  }

}

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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);
  }
}

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Output

Apple iPhone 6s Screen Width = 750
Apple iPhone 16s Screen Width = 0

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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;
}

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8.2 Method Return Type

public Optional<ScreenResolution> getResolution() {
	return resolution;
}

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8.3 Constructor Parameter

public DisplayFeatures(String size, Optional<ScreenResolution> resolution){
	this.size = size;
	this.resolution = resolution;
}

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8.4 Variable Declaration

private Optional<ScreenResolution> resolution;

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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/