Java 8 Optional Example | Avoid NullPointerException
October 28, 2014
Before Java 8
String s="None";
if(person !=null) {
if (country != null) {
if (primeMinister != null){
System.out.println(name);
}
}
}
In Java 8
String pmName= person.flatMap(Person::getCountry).flatMap(Country::getPrimeMinister)
.map(PrimeMinister::getName).orElse("None");
Optional.of()
of() method creates and returns the Optional instance for the given class. We can apply other method of Optional class.Optional.map()
map() method runs the given method in the argument if the instance is not null otherwise it returns empty Optional instance. The argument which is a function cannot have Optional mapper.Optional.orElse()
It returns the value in the Optional instance for the mapping method otherwise it returns the value provided in orElse() argument.Now find a class named PrimeMinister.
PrimeMinister.java
package com.concretepage.util;
public class PrimeMinister {
String name;
public PrimeMinister(){}
public PrimeMinister(String name){
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
OptionalDemoOne.java
package com.concretepage.util;
import java.util.Optional;
public class OptionalDemoOne {
public static void main(String[] args) {
Optional<PrimeMinister> pm = Optional.of(new PrimeMinister());
String pmName = pm.map(PrimeMinister::getName).orElse("None");
System.out.println(pmName);
//Assign Some Value to PrimeMinister.name
pm = Optional.of(new PrimeMinister("Narendra Modi"));
pmName = pm.map(PrimeMinister::getName).orElse("None");
System.out.println(pmName);
}
}
None Narendra Modi
Optional.flatMap()
flatMap () method is same as map() method but the difference is that the method argument which is a function must have Optional mapper.Find some more classes. We have a Country class.
Country.java
package com.concretepage.util;
import java.util.Optional;
public class Country {
Optional<PrimeMinister> primeMinister;
public Country(){}
public Country(Optional<PrimeMinister> primeMinister){
this.primeMinister = primeMinister;
}
public Optional<PrimeMinister> getPrimeMinister() {
return primeMinister;
}
public void setPrimeMinister(Optional<PrimeMinister> primeMinister) {
this.primeMinister = primeMinister;
}
}
Person.java
package com.concretepage.util;
import java.util.Optional;
public class Person {
Optional<Country> country;
public Person(){}
public Person(Optional<Country> country){
this.country = country;
}
public Optional<Country> getCountry() {
return country;
}
public void setCountry(Optional<Country> country) {
this.country = country;
}
}
OptionalDemoTwo.java
package com.concretepage.util;
import java.util.Optional;
public class OptionalDemoTwo {
public static void main(String[] args) {
Optional<PrimeMinister> primeMinister = Optional.of(new PrimeMinister("Narendra Modi"));
Optional<Country> country = Optional.of(new Country(primeMinister));
Optional<Person> person = Optional.of(new Person(country));
String pmName= person.flatMap(Person::getCountry).flatMap(Country::getPrimeMinister)
.map(PrimeMinister::getName).orElse("None");
System.out.println(pmName);
}
}
Narendra Modi
Optional.filter()
filter() method takes Predicate instance as an argument. The value in Optional instance is filtered and if filtered value is not empty then value is returned otherwise empty Optional instance is returned.Optionalfilter.java
package com.concretepage.util;
import java.util.Optional;
import java.util.function.Predicate;
public class Optionalfilter {
public static void main(String[] args) {
Optional<PrimeMinister> pm = Optional.of(new PrimeMinister("Narendra Modi"));
//Using Optional.filter
Predicate<PrimeMinister> pmPredicate = p-> p.getName().length() > 15;
System.out.println(pm.filter(pmPredicate));
}
}
Optional.empty
Optional.ifPresent()
ifPresent() method takes Consumer instance as an argument and if value is present then it run the given consumer passed as an argument otherwise do nothing.OptionalifPresent.java
package com.concretepage.util;
import java.util.Optional;
import java.util.function.Consumer;
public class OptionalifPresent {
public static void main(String[] args) {
Optional<PrimeMinister> pm = Optional.of(new PrimeMinister("Narendra Modi"));
//Using Optional.ifPresent
Consumer<PrimeMinister> pmConsumer = (PrimeMinister p) -> System.out.println(p.getName());
pm.ifPresent(pmConsumer);
}
}
Narendra Modi
Optional.isPresent()
It returns true and false value. If value is present, then returns true otherwise false.
package com.concretepage.util;
import java.util.Optional;
public class OptionalisPresent {
public static void main(String[] args) {
Optional<PrimeMinister> pm = Optional.of(new PrimeMinister("Narendra Modi"));
//Using Optional.isPresent
System.out.println(pm.isPresent());
}
}
true
