Comparable vs Comparator

Comparable

• It present in Java.lang Package.
• It Contains only one Method.
• Comparable can be used for natural or default sorting ordering.

        compareTo()

Method

• public int compareTo(Object obj1,obj2)

obj1.compareTo(obj2)

• Return(-ve), iff obj1 has to come before obj2.
• Return(+ve), iff obj1 has to come after obj2.
• Return(0),  iff obj1 & obj2 are equal.

foreg:

• System.out.println("A".compareTo("z")); 

Return value is Negative/(-ve).

• System.out.println("z".compareTo("k")); 

Return value is positivetive/(+ve)

• System.out.println("A".compareTo("A")); 

Return value is Zero/(0)

• System.out.println("A".compareTo("null"));

Return value is Null Pointer Exception.

Object1:-The Object, which is to be Inserted.

Object2:-The Object, which is already Inserted. 

If We are Depending on Default Natural Sorting Order while adding object in to the TreeSet JVM will call (compareTo) method.

Note:

• If Default Natural Sorting Order not available or if we are not satisfied with Default Natural Sorting Order, than we can go for Customizer Sorting by using Comparator.

Comparator

• It present in java.util.Package.
• Comparator can be used for custom ordering.
• It defines Two Methods. 
1. compare() 
2. equals()

Method

1. public int compare(object obj1, obj2)

obj1.compareTo(obj2)

• Return(-ve), iff obj1 has to come before obj2.
• Return(+ve), iff obj1 has to come after obj2.
• Return(0),  iff obj1 & obj2 are equal.

  2.public boolean equals(obj)

• Whenever we are implementing Comparator interface compulsory we should provide implementation only for compare method.
• we are not required to provide implementation for equals method .Because it is already available to our class from object class through Inheritance. 

For eg of Comparator

• Write a program To Insert Objects into the TreeSet, Where the Sorting order is Descending Order

Output is

• If we are not Passing comparator Object than internally JVM will call comparatorTo method, which is meant for Default Natural Sorting Order, In this case the output is 
• [0,5,10,15,20]
• If we are passing compare object than, JVM will call compare method which meant for Customizer Sorting in this case output is 
• [20,15,10.5,0]

Various implementation of compare method

for eg:    Main class

       

result is Ascending Order

• when you return I1(-ve) & I2(+ve)

Result is Descending 

• when you return I2(-ve) & I1(+ve

Result is Ascending 

• when you return -1

Result is [Rverse of Inversion Order]

• when you return +1

Result is [Insertion Order]

• when you return 0

Result is[Only First element will be insertion order all remaining consider as Duplicates]

Difference B/w Comparable & Comparator