Comparable and Comparator in Java

// Example of Comparable in collection

import java.util.ArrayList;
import java.util.Collections;

public class ArrayList3 {
public static void main(String as[]) {
ArrayList<Student1> al = new ArrayList<>();
al.add(new Student1(1,"vcd","dvrns"));
al.add(new Student1(10,"avcd","avrns"));
al.add(new Student1(3,"gvcd","cvrns"));
al.add(new Student1(12,"cvcd","vrns"));
System.out.println("Before Sorting");
for(Student1 s: al) {
System.out.println(s.rn+" "+s.name+" "+s.addr);
}
System.out.println("After Sorting");
Collections.sort(al);
for(Student1 s: al) {
System.out.println(s.rn+" "+s.name+" "+s.addr);
}
}
}

class Student1 implements Comparable<Student1> {
int rn;
String name;
String addr;
Student1(int a, String b, String c){
rn = a;
name = b;
addr = c;
}
@Override
public int compareTo(Student1 o) {
if(o.rn > rn)
return 1;
return -1;
}
}

// Example of Comparator in collection

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

public class ArrayList4 {
@SuppressWarnings("unchecked")
public static void main(String as[]) {
ArrayList<Student4> al = new ArrayList<>();
al.add(new Student4(1,"vcd","dvrns"));
al.add(new Student4(10,"avcd","avrns"));
al.add(new Student4(3,"gvcd","cvrns"));
al.add(new Student4(12,"cvcd","vrns"));
System.out.println("Before Sorting");
for(Student4 s: al) {
System.out.println(s.rn+" "+s.name+" "+s.addr);
}
System.out.println("rn Sorting");
Collections.sort(al, new rnCompare());
for(Student4 s: al) {
System.out.println(s.rn+" "+s.name+" "+s.addr);
}

System.out.println("name Sorting");
Collections.sort(al, new nameCompare());
for(Student4 s: al) {
System.out.println(s.rn+" "+s.name+" "+s.addr);
}
}
}

class Student4 {
int rn;
String name;
String addr;

public Student4(int a, String n, String b) {
rn = a;
name = n;
addr = b;
}

}

class rnCompare implements Comparator {
public int compare(Object o1, Object o2) {
Student4 s1 = (Student4)o1;
Student4 s2 = (Student4)o2;
if(s1.rn > s2.rn)
return 1;
return -1;
}
}

class nameCompare implements Comparator {
public int compare(Object o1, Object o2) {
Student4 s1 = (Student4)o1;
Student4 s2 = (Student4)o2;
return s1.name.compareTo(s2.name);
}
}