Why do we use comparator in Java?

Comparator can be used to compare instances of different classes. Comparable is implemented by class which need to define a natural ordering for its objects. Like String implements Comparable. In case one wants a different sorting order then he can implement comparator and define its own way of comparing two instances.

Also know, what is the use of comparator in Java?

Java Comparator interface is used to order the objects of a user-defined class. This interface is found in java. util package and contains 2 methods compare(Object obj1,Object obj2) and equals(Object element).

Beside above, how do you implement a comparator in Java? Using Comparator

Create a class that implements Comparator (and thus the compare() method that does the work previously done by compareTo()).
Make an instance of the Comparator class.
Call the overloaded sort() method, giving it both the list and the instance of the class that implements Comparator.

In this regard, what is the use of comparator and comparable in Java?

Comparable v/s Comparator in Java Comparable interface is used to sort the objects with natural ordering. Comparator in Java is used to sort attributes of different objects. Comparable interface compares “this” reference with the object specified. Comparator in Java compares two different class objects provided.

How does a comparator work internally?

Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. and boolean equals(Object obj); Comparator provides multiple sorting sequence. In other words, we can sort the collection on the basis of multiple elements such as id, name and price etc.

37 Related Question Answers Found

How do you use compareTo?

The Java String compareTo() method is used for comparing two strings lexicographically. Each character of both the strings is converted into a Unicode value for comparison. If both the strings are equal then this method returns 0 else it returns positive or negative value.

How does a TreeMap work?

TreeMap in Java. The TreeMap is used to implement Map interface and NavigableMap along with the Abstract Class. Also, all its elements store in the TreeMap are sorted by key. TreeMap performs sorting in natural order on its key, it also allows you to use Comparator for custom sorting implementation.

Can we sort HashMap in Java?

HashMap is not meant to keep entries in sorted order, but if you have to sort HashMap based upon keys or values, you can do that in Java. Sorting HashMap on keys is quite easy, all you need to do is to create a TreeMap by copying entries from HashMap. This is similar of how you sort an ArrayList in Java.

How does the comparator work?

Comparator Circuit. A comparator circuit compares two voltages and outputs either a 1 (the voltage at the plus side; VDD in the illustration) or a 0 (the voltage at the negative side) to indicate which is larger. Comparators are often used, for example, to check whether an input has reached some predetermined value.

What is serialization in Java?

Serialization is a mechanism of converting the state of an object into a byte stream. Deserialization is the reverse process where the byte stream is used to recreate the actual Java object in memory. To make a Java object serializable we implement the java. io. Serializable interface.

What is singleton class in Java?

Singleton Class in Java. In object-oriented programming, a singleton class is a class that can have only one object (an instance of the class) at a time. To design a singleton class: Make constructor as private. Write a static method that has return type object of this singleton class.

What does compareTo return in Java?

The compareTo method is used when we need to determine the order of Strings lexicographically. It compares char values similar to the equals method. The compareTo method returns a negative integer if the first String object precedes the second string. It returns zero if the 2 strings being compared are equal.

How do you sort a string in Java?

Method 1(natural sorting) :

Apply toCharArray() method on input string to create a char array for input string.
Use Arrays. sort(char c[]) method to sort char array.
Use String class constructor to create a sorted string from char array.

Is comparator an interface?

Method 2: Using comparator interface- Comparator interface is used to order the objects of user-defined class. This interface is present in java. util package and contains 2 methods compare(Object obj1, Object obj2) and equals(Object element). Using comparator, we can sort the elements based on data members.

What is the difference between Array and ArrayList?

1- First and Major difference between Array and ArrayList in Java is that Array is a fixed length data structure while ArrayList is a variable length Collection class. You can not change length of Array once created in Java but ArrayList re-size itself when gets full depending upon capacity and load factor.

How do you compare two different objects?

If the two objects have the same values, equals() will return true . In the second comparison, equals() checks to see whether the passed object is null, or if it's typed as a different class. If it's a different class then the objects are not equal. Finally, equals() compares the objects' fields.

Why is string immutable in Java?

The string is Immutable in Java because String objects are cached in String pool. Another reason of why String class is immutable could die due to HashMap. Since Strings are very popular as HashMap key, it's important for them to be immutable so that they can retrieve the value object which was stored in HashMap.

What is natural sorting order in Java?

Java allows you to sort your object in natural order by implementing Comparable interface. Comparable is used to provide natural order of sorting to objects e.g. numeric order is natural order for numbers, alphabetic order is natural order for String and chronological order is natural for dates.

What is Hashcode in Java?

Answer: The hashcode of a Java Object is simply a number, it is 32-bit signed int, that allows an object to be managed by a hash-based data structure. We know that hash code is an unique id number allocated to an object by JVM. If two objects are equals then these two objects should return same hash code.

What is cloneable in Java?

Cloneable interface : Cloneable interface is present in java. lang package. There is a method clone() in Object class. A class that implements the Cloneable interface indicates that it is legal for clone() method to make a field-for-field copy of instances of that class.

What is difference between compare and compareTo in Java?

compareTo() is called on one object, to compare it to another object. compare() is called on some object to compare two other objects. The difference is where the logic that does actual comparison is defined. The relationship of the object having this method and its collaborators is different.

What is map in Java?

A Map is an object that maps keys to values. A map cannot contain duplicate keys: Each key can map to at most one value. It models the mathematical function abstraction. The Java platform contains three general-purpose Map implementations: HashMap , TreeMap , and LinkedHashMap .