ConcretePage.comJava 8 UnaryOperator and BinaryOperator
November 22, 2014
UnaryOperator
java.util.function.UnaryOperator is a java 8 functional interface that extends java.util.function.Function. UnaryOperator is used to work on a single operand. It returns the same type as an operand. UnaryOperator can be used as lambda expression to pass as an argument. While defining UnaryOperator, we need to define Function.apply(Object) where Function will be the instance of UnaryOperator. Find the example.UnaryOperatorDemo.java
package com.concretepage.util.stream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.UnaryOperator;
public class UnaryOperatorDemo {
public static void main(String[] args) {
List<Integer> list = Arrays.asList(10,20,30,40,50);
UnaryOperator<Integer> unaryOpt = i->i*i;
unaryOperatorFun(unaryOpt, list).forEach(x->System.out.println(x));
}
private static List<Integer> unaryOperatorFun(UnaryOperator<Integer> unaryOpt, List<Integer> list){
List<Integer> uniList = new ArrayList<>();
list.forEach(i->uniList.add(unaryOpt.apply(i)));
return uniList;
}
}
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BinaryOperator
java.util.function.BinaryOperator is a functional interface that can be assigned as lambda expression. BinaryOperator extends java.util.function.BiFunction. It accepts two operands of the same type and process it and then returns results of the same type as operands.BinaryOperatorDemo.java
package com.concretepage.util.stream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.BinaryOperator;
public class BinaryOperatorDemo {
public static void main(String[] args) {
Map<String,String> map = new HashMap<>();
map.put("X", "A");
map.put("Y", "B");
map.put("Z", "C");
BinaryOperator<String> binaryOpt = (s1,s2)-> s1+"-"+s2;
binaryOperatorFun(binaryOpt, map).forEach(x->System.out.println(x));
}
private static List<String> binaryOperatorFun(BinaryOperator<String> binaryOpt, Map<String,String> map){
List<String> biList = new ArrayList<>();
map.forEach((s1,s2)->biList.add(binaryOpt.apply(s1,s2)));
return biList;
}
}
X-A Y-B Z-C
BinaryOperator.maxBy and BinaryOperator.minBy
BinaryOperator.maxBy accepts a Compotator and returns BinaryOperator which will return maximum between two elements. In the same way, BinaryOperator.minBy is used to get minimum between two elements.MaxByMinBy.java
package com.concretepage.util;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.function.BinaryOperator;
import java.util.stream.Collectors;
public class MaxByMinBy {
public static void main(String[] args) {
Student s1 = new Student("Shyam", 22,"A");
Student s2 = new Student("Ram",23,"A");
Student s3 = new Student("Mohan",22,"B");
Student s4 = new Student("Ramesh",21,"B");
List<Student> list = Arrays.asList(s1,s2,s3,s4);
Comparator<Student> ageComparator = Comparator.comparing(Student::getAge);
//Using BinaryOperator.maxBy
System.out.println("---BinaryOperator.maxBy---");
Map<String, Optional<Student>> eldestByClass = list.stream().collect(Collectors.groupingBy(Student::getClassName,
Collectors.reducing(BinaryOperator.maxBy(ageComparator))));
eldestByClass.forEach((k,v)->System.out.println("Class:"+k+" Age:"+
((Optional<Student>)v).get().getAge()+" Name:"+((Optional<Student>)v).get().getName()));
//Using BinaryOperator.minBy
System.out.println("---BinaryOperator.minBy---");
Map<String, Optional<Student>> youngestByClass = list.stream().collect(Collectors.groupingBy(Student::getClassName,
Collectors.reducing(BinaryOperator.minBy(ageComparator))));
youngestByClass.forEach((k,v)->System.out.println("Class:"+k+" Age:"+
((Optional<Student>)v).get().getAge()+" Name:"+((Optional<Student>)v).get().getName()));
}
}
Student.java
package com.concretepage.util;
public class Student {
private String name;
private Integer age;
private String className;
public Student(String name,Integer age, String className){
this.name=name;
this.age=age;
this.className = className;
}
public String getName() {
return name;
}
public Integer getAge() {
return age;
}
public String getClassName() {
return className;
}
}
---BinaryOperator.maxBy--- Class:A Age:23 Name:Ram Class:B Age:22 Name:Mohan ---BinaryOperator.minBy--- Class:A Age:22 Name:Shyam Class:B Age:21 Name:Ramesh
