Collections.max in Java
February 06, 2022
Collections.max method.
a. Max element is found on the basis of
Comparable interface implemented by class of collection element. Pass Collection instance.
static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll)
Comparable interface. All elements in the collection must be mutually comparable i.e. e1.compareTo(e2) must not throw a ClassCastException.
b. Max element of the collection is found on the basis of specified
Comparator instance. Pass Collection and Comparator instances.
public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp)
comp.compare(e1, e2) must not throw a ClassCastException for any elements e1 and e2 in the collection.
Example-1
CollectionsMax1.java
package com.concretepage;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class CollectionsMax1 {
public static void main(String[] args) {
List<Integer> numList = new ArrayList<>();
numList.add(10);
numList.add(30);
numList.add(20);
int numMax = Collections.max(numList);
System.out.println(numMax); // Output: 30
List<String> strList = new ArrayList<>();
strList.add("Mohan");
strList.add("Ramesh");
strList.add("Mahesh");
String strMax = Collections.max(strList);
System.out.println(strMax); // Output: Ramesh
}
}
Example-2
CollectionsMax2.java
package com.concretepage;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class CollectionsMax2 {
public static void main(String[] args) {
User u1 = new User("Rohit", 20);
User u2 = new User("Vivek", 22);
User u3 = new User("Raju", 25);
List<User> list = new ArrayList<User>();
list.add(u1);
list.add(u2);
list.add(u3);
User maxUser = Collections.max(list);
System.out.println(maxUser.name); // Output: Vivek
}
}
class User implements Comparable<User> {
String name;
int age;
public User(String name, int age) {
this.name = name;
this.age = age;
}
@Override
public int compareTo(User o) {
return name.compareTo(o.name);
}
}
Example-3
Here we will passComparator instances to Collection to find max element.
CollectionsMax3.java
package com.concretepage;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class CollectionsMax3 {
public static void main(String[] args) {
Person p1 = new Person("Rohit", 20);
Person p2 = new Person("Vivek", 22);
Person p3 = new Person("Raju", 25);
List<Person> list = new ArrayList<Person>();
list.add(p1);
list.add(p2);
list.add(p3);
Comparator<Person> compByName = Comparator.comparing(Person::getName);
Person maxUserByName = Collections.max(list, compByName);
System.out.println(maxUserByName.getName()); // Output: Vivek
Comparator<Person> compByAge = Comparator.comparing(Person::getAge);
Person maxUserByAge = Collections.max(list, compByAge);
System.out.println(maxUserByAge.getName()); // Output: Raju
}
}
class Person {
private String name;
private int age;
public String getName() {
return name;
}
public int getAge() {
return age;
}
public Person(String name, int age) {
this.name = name;
this.age = age;
}
}
