Java Advanced Sorting

Java Advanced Sorting

In Java Advanced Sorting objects requires defining how objects should be compared.
Java provides Comparable and Comparator interfaces for custom sorting logic.

1. `Comparable` Interface

Comparable defines a natural order for objects.

Package: java.lang
Contains method:

Return values:
- Negative → current object < o
- Zero → current object = o
- Positive → current object > o

Example: Using Comparable

import java.util.*;

class Student implements Comparable<Student> {
String name;
int age;

Student(String name, int age) {
this.name = name;
this.age = age;
}

// Natural ordering by age
public int compareTo(Student other) {
return this.age - other.age; // ascending order
}

public String toString() {
return name + " (" + age + ")";
}
}

public class ComparableExample {
public static void main(String[] args) {
List<Student> students = new ArrayList<>();
students.add(new Student("Vipul", 25));
students.add(new Student("Anita", 22));
students.add(new Student("Rahul", 28));

Collections.sort(students); // Uses compareTo
System.out.println("Sorted by age: " + students);
}
}

import java.util.*;

class Student implements Comparable<Student> {

String name;

int age;

Student(String name, int age) {

this.name = name;

this.age = age;

}

// Natural ordering by age

public int compareTo(Student other) {

return this.age - other.age; // ascending order

}

public String toString() {

return name + " (" + age + ")";

}

public class ComparableExample {

public static void main(String[] args) {

List<Student> students = new ArrayList<>();

students.add(new Student("Vipul", 25));

students.add(new Student("Anita", 22));

students.add(new Student("Rahul", 28));

Collections.sort(students); // Uses compareTo

System.out.println("Sorted by age: " + students);

}

2. `Comparator` Interface

Comparator allows custom sorting logic, independent of natural order.

Package: java.util
Methods:
Java
int compare(T o1, T o2) boolean equals(Object obj) // optional
1
2
int compare(T o1, T o2)
boolean equals(Object obj) // optional

Example: Using Comparator

import java.util.*;

class Student {
String name;
int age;

Student(String name, int age) {
this.name = name;
this.age = age;
}

public String toString() {
return name + " (" + age + ")";
}
}

public class ComparatorExample {
public static void main(String[] args) {
List<Student> students = new ArrayList<>();
students.add(new Student("Vipul", 25));
students.add(new Student("Anita", 22));
students.add(new Student("Rahul", 28));

// Sort by name
students.sort(new Comparator<Student>() {
public int compare(Student s1, Student s2) {
return s1.name.compareTo(s2.name);
}
});

System.out.println("Sorted by name: " + students);

// Using lambda (Java 8+)
students.sort((s1, s2) -> s2.age - s1.age); // descending by age
System.out.println("Sorted by age descending: " + students);
}
}

import java.util.*;

class Student {

String name;

int age;

Student(String name, int age) {

this.name = name;

this.age = age;

}

public String toString() {

return name + " (" + age + ")";

}

public class ComparatorExample {

public static void main(String[] args) {

List<Student> students = new ArrayList<>();

students.add(new Student("Vipul", 25));

students.add(new Student("Anita", 22));

students.add(new Student("Rahul", 28));

// Sort by name

students.sort(new Comparator<Student>() {

public int compare(Student s1, Student s2) {

return s1.name.compareTo(s2.name);

}

});

System.out.println("Sorted by name: " + students);

// Using lambda (Java 8+)

students.sort((s1, s2) -> s2.age - s1.age); // descending by age

System.out.println("Sorted by age descending: " + students);

}

Comparator is useful for multiple sorting criteria
Can be implemented as anonymous class or lambda expression

3. Common Sorting Techniques

Technique	Description
`Comparable`	Define natural order inside class
`Comparator`	Define custom order outside class
`Collections.sort(list)`	Sort list using natural/comparator order
`list.sort(Comparator)`	Java 8+ lambda sorting

4. Example: Multiple Sorting Criteria

comparing() → primary sort
thenComparing() → secondary sort
Works well with Java 8+ Streams API

Summary

Comparable → single natural ordering (inside class)
Comparator → multiple/custom orderings (outside class)
Java 8+ allows lambda expressions for concise comparator implementation
Use Collections.sort() or list.sort() for sorting

Java Advanced Sorting

Java Advanced Sorting

1. Comparable Interface

Example: Using Comparable

2. Comparator Interface

Example: Using Comparator

3. Common Sorting Techniques

4. Example: Multiple Sorting Criteria

Summary

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1. `Comparable` Interface

2. `Comparator` Interface