Java this Keyword Last Updated : 02 Jun, 2025 Summarize Suggest changes Share Like Article Like Report In Java, "this" is a reference variable that refers to the current object, or can be said "this" in Java is a keyword that refers to the current object instance. It is mainly used to,Call current class methods and fieldsTo pass an instance of the current class as a parameterTo differentiate between the local and instance variables. Using "this" reference can improve code readability and reduce naming conflicts.Java "this" Reference Example The this keyword can be used to access instance variables and methods of the object on which the method or constructor is being invoked.Below is the implementation of "this" reference: Java // Java program to demonstrate // this reference // Driver Class public class Person { // Fields Declared String name; int age; // Constructor Person(String name, int age) { this.name = name; this.age = age; } // Getter for name public String get_name() { return name; } // Setter for name public void change_name(String name) { this.name = name; } // Method to Print the Details of // the person public void printDetails() { System.out.println("Name: " + this.name); System.out.println("Age: " + this.age); System.out.println(); } // main function public static void main(String[] args) { // Objects Declared Person first = new Person("ABC", 18); Person second = new Person("XYZ", 22); first.printDetails(); second.printDetails(); first.change_name("PQR"); System.out.println("Name has been changed to: " + first.get_name()); } } OutputName: ABC Age: 18 Name: XYZ Age: 22 Name has been changed to: PQR Explanation: Here, we have defined a "Person" class with two private fields "name" and "age". We have defined the Person class constructor to initialize these fields using "this" keyword. We have also defined "getter and setter" methods for these fields which use this keyword to refer to the current object instance.In the printDetails() method, we have used "this" keyword to refer to the current object instance and print its name, age, and object reference.In the Main class, we have created two Person objects and called the printDetails() method on each object. The output shows the name, age, and object reference of each object instance.Methods to Use "this" in JavaFollowing are the ways to use the "this" keyword in Java mentioned below:Using "this" keyword to refer to current class instance variables.Using this() to invoke the current class constructorUsing 'this' keyword to return the current class instance Using 'this' keyword as the method parameterUsing 'this' keyword to invoke the current class method Using 'this' keyword as an argument in the constructor call1. Using "this" to Refer to Current Class Instance Variables Java // Java program for using "this" keyword to // refer current class instance variables class Geeks { int a; int b; // Parameterized constructor Geeks(int a, int b) { this.a = a; this.b = b; } void display() { // Displaying value of variables a and b System.out.println("a = " + a + " b = " + b); } public static void main(String[] args) { Geeks object = new Geeks(10, 20); object.display(); } } Outputa = 10 b = 20 2. Using this() to Invoke Current Class Constructor Java // Java program for using this() to // invoke current class constructor class Geeks { int a; int b; // Default constructor Geeks() { this(10, 20); System.out.println( "Inside default constructor \n"); } // Parameterized constructor Geeks(int a, int b) { this.a = a; this.b = b; System.out.println( "Inside parameterized constructor"); } public static void main(String[] args) { Geeks object = new Geeks(); } } OutputInside parameterized constructor Inside default constructor 3. Using "this" Keyword to Return the Current Class Instance Java // Java program for using "this" keyword // to return the current class instance class Geeks { int a; int b; // Default constructor Geeks() { a = 10; b = 20; } // Method that returns current class instance Geeks get() { return this; } // Displaying value of variables a and b void display() { System.out.println("a = " + a + " b = " + b); } public static void main(String[] args) { Geeks object = new Geeks(); object.get().display(); } } Outputa = 10 b = 20 4. Using "this" Keyword as a Method Parameter Java // Java program for using "this" // keyword as method parameter class Geeks { int a; int b; // Default constructor Geeks() { a = 10; b = 20; } // Method that receives "this" // keyword as parameter void display(Geeks obj) { System.out.println("a = " + obj.a + " b = " + obj.b); } // Method that returns current class instance void get() { display(this); } // main function public static void main(String[] args) { Geeks object = new Geeks(); object.get(); } } Outputa = 10 b = 20 5. Using "this" Keyword to Invoke the Current Class Method Java // Java program for using this to invoke current // class method class Geeks { void display() { // calling function show() this.show(); System.out.println("Inside display function"); } void show() { System.out.println("Inside show function"); } public static void main(String args[]) { Geeks g1 = new Geeks(); g1.display(); } } OutputInside show function Inside display function 6. Using "this" Keyword as an Argument in the Constructor Call Java // Java program for using this as an // argument in constructor call // Class with object of Class B as its data member class A { B obj; // Parameterized constructor with object of B // as a parameter A(B obj) { this.obj = obj; // calling display method of class B obj.display(); } } class B { int x = 5; // Default Constructor that create an object of A // with passing this as an argument in the // constructor B() { A obj = new A(this); } // method to show value of x void display() { System.out.println("Value of x in Class B : " + x); } public static void main(String[] args) { B obj = new B(); } } OutputValue of x in Class B : 5 Advantages of Using "this" ReferenceThere are many advantages of using "this" reference in Java as mentioned below:It helps to distinguish between instance variables and local variables with the same name.It can be used to pass the current object as an argument to another method.It can be used to return the current object from a method.It can be used to invoke a constructor from another overloaded constructor in the same class.Disadvantages of Using "this" ReferenceAlthough "this" reference comes with many advantages there are disadvantages of also:Overuse of this can make the code harder to read and understand.Using this unnecessarily can add unnecessary overhead to the program.Using this in a static context results in a compile-time error.Overall, this keyword is a useful tool for working with objects in Java, but it should be used judiciously and only when necessary. 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Thread.start() vs Thread.run() MethodThread.start()Thread.run()Creates a new thread and the run() method is ex 4 min read Java Searching ProgramsJava Program for Linear SearchLinear Search is the simplest searching algorithm that checks each element sequentially until a match is found. It is good for unsorted arrays and small datasets.Given an array a[] of n elements, write a function to search for a given element x in a[] and return the index of the element where it is 2 min read Binary Search in JavaBinary search is a highly efficient searching algorithm used when the input is sorted. It works by repeatedly dividing the search range in half, reducing the number of comparisons needed compared to a linear search. Here, we are focusing on finding the middle element that acts as a reference frame t 6 min read Java Program To Recursively Linearly Search An Element In An ArrayGiven an array arr[] of n elements, write a recursive function to search for a given element x in the given array arr[]. If the element is found, return its index otherwise, return -1.Input/Output Example:Input : arr[] = {25, 60, 18, 3, 10}, Element to be searched x = 3Output : 3 (index )Input : arr 3 min read Java 1-D Array ProgramsCheck If a Value is Present in an Array in JavaGiven an array of Integers and a key element. Our task is to check whether the key element is present in the array. If the element (key) is present in the array, return true; otherwise, return false.Example: Input: arr[] = [3, 5, 7, 2, 6, 10], key = 7Output: Is 7 present in the array: trueInput: arr 8 min read Java Program to Find Largest Element in an ArrayFinding the largest element in an array is a common programming task. There are multiple approaches to solve it. In this article, we will explore four practical approaches one by one to solve this in Java.Example Input/Output:Input: arr = { 1, 2, 3, 4, 5}Output: 5Input: arr = { 10, 3, 5, 7, 2, 12}Ou 4 min read Arrays.sort() in JavaThe Arrays.sort() method is used for sorting the elements in an Array. It has two main variations: Sorting the entire array (it may be an integer or character array) Sorting a specific range by passing the starting and ending indices.Below is a simple example that uses the sort() method to arrange a 6 min read Java Program to Sort the Elements of an Array in Descending OrderHere, we will sort the array in descending order to arrange elements from largest to smallest. The simple solution is to use Collections.reverseOrder() method. Another way is sorting in ascending order and reversing.1. Using Collections.reverseOrder()In this example, we will use Collections.reverseO 2 min read Java Program to Sort the Elements of an Array in Ascending OrderHere, we will sort the array in ascending order to arrange elements from smallest to largest, i.e., ascending order. So the easy solution is that we can use the Array.sort method. We can also sort the array using Bubble sort.1. Using Arrays.sort() MethodIn this example, we will use the Arrays.sort() 2 min read Remove duplicates from Sorted ArrayGiven a sorted array arr[] of size n, the goal is to rearrange the array so that all distinct elements appear at the beginning in sorted order. Additionally, return the length of this distinct sorted subarray.Note: The elements after the distinct ones can be in any order and hold any value, as they 7 min read Java Program to Merge Two ArraysIn Java, merging two arrays is a good programming question. We have given two arrays, and our task is to merge them, and after merging, we need to put the result back into another array. In this article, we are going to discuss different ways we can use to merge two arrays in Java.Let's now see the 5 min read Java Program to Check if two Arrays are Equal or notIn Java, comparing two arrays means checking if they have the same length and identical elements. This checking process ensures that both arrays are equivalent in terms of content and structure.Example:In Java, the simplest way to check if two arrays are equal in Java is by using the built-in Arrays 3 min read Remove all Occurrences of an Element from Array in JavaIn Java, removing all occurences of a given element from an array can be done using different approaches that are,Naive approach using array copyJava 8 StreamsUsing ArrayList.removeAll()Using List.removeIf()Problem Stament: Given an array and a key, the task is to remove all occurrences of the speci 5 min read Java Program to Find Common Elements Between Two ArraysGiven two arrays and our task is to find their common elements. Examples:Input: Array1 = ["Article", "for", "Geeks", "for", "Geeks"], Array2 = ["Article", "Geeks", "Geeks"]Output: [Article, Geeks]Input: Array1 = ["a", "b", "c", "d", "e", "f"], Array2 = ["b", "d", "e", "h", "g", "c"]Output: [b, c, d, 4 min read Array Copy in JavaIn Java, copying an array can be done in several ways, depending on our needs such as shallow copy or deep copy. In this article, we will learn different methods to copy arrays in Java.Example:Assigning one array to another is an incorrect approach to copying arrays. It only creates a reference to t 6 min read Java Program to Left Rotate the Elements of an ArrayIn Java, left rotation of an array involves shifting its elements to the left by a given number of positions, with the first elements moving around to the end. There are different ways to left rotate the elements of an array in Java.Example: We can use a temporary array to rotate the array left by " 5 min read Java 2-D Arrays (Matrix) ProgramsPrint a 2D Array or Matrix in JavaIn this article, we will learn to Print 2 Dimensional Matrix. 2D-Matrix or Array is a combination of Multiple 1 Dimensional Arrays. In this article we cover different methods to print 2D Array. When we print each element of the 2D array we have to iterate each element so the minimum time complexity 4 min read Java Program to Add two MatricesGiven two matrices A and B of the same size, the task is to add them in Java. Examples: Input: A[][] = {{1, 2}, {3, 4}} B[][] = {{1, 1}, {1, 1}} Output: {{2, 3}, {4, 5}} Input: A[][] = {{2, 4}, {3, 4}} B[][] = {{1, 2}, {1, 3}} Output: {{3, 6}, {4, 7}}Program to Add Two Matrices in JavaFollow the Ste 2 min read Sorting a 2D Array according to values in any given column in JavaWe are given a 2D array of order N X M and a column number K ( 1<=K<=m). Our task is to sort the 2D array according to values in Column K.Examples:Input: If our 2D array is given as (Order 4X4) 39 27 11 42 10 93 91 90 54 78 56 89 24 64 20 65Sorting it by values in column 3 Output: 39 27 11 422 3 min read Java Program to Check if two Arrays are Equal or notIn Java, comparing two arrays means checking if they have the same length and identical elements. This checking process ensures that both arrays are equivalent in terms of content and structure.Example:In Java, the simplest way to check if two arrays are equal in Java is by using the built-in Arrays 3 min read Java Program to Find Transpose of MatrixTranspose of a matrix is obtained by changing rows to columns and columns to rows. In other words, the transpose of A[ ][ ] is obtained by changing A[i][j] to A[j][i]. Example of First Transpose of MatrixInput: [ [ 1 , 2 , 3 ] , [ 4 , 5 , 6 ] , [ 7 , 8 , 9 ] ]Output: [ [ 1 , 4 , 7 ] , [ 2 , 5 , 8 ] 5 min read Java Program to Find the Determinant of a MatrixThe determinant of a matrix is a special calculated value that can only be calculated if the matrix has same number of rows and columns (square matrix). It is helpful in determining the system of linear equations, image processing, and determining whether the matrix is singular or non-singular.In th 5 min read Java Program to Find the Normal and Trace of a MatrixIn Java, when we work with matrices, there are two main concepts, and these concepts are Trace and Normal of a matrix. In this article, we will learn how to calculate them and discuss how to implement them in code. Before moving further, let's first understand what a matrix is. What is a Matrix?A ma 3 min read Java Program to Print Boundary Elements of the MatrixIn this article, we are going to learn how to print only the boundary elements of a given matrix in Java. Boundary elements mean the elements from the first row, last row, first column, and last column.Example:Input : 1 2 3 4 5 6 7 8 9Output: 1 2 3 4 6 7 8 9Now, let's understand the approach we are 3 min read Java Program to Rotate Matrix ElementsA matrix is simply a two-dimensional array. So, the goal is to deal with fixed indices at which elements are present and to perform operations on indexes such that elements on the addressed should be swapped in such a manner that it should look out as the matrix is rotated.For a given matrix, the ta 6 min read Java Program to Compute the Sum of Diagonals of a MatrixFor a given 2D square matrix of size N*N, our task is to find the sum of elements in the Principal and Secondary diagonals. For example, analyze the following 4 × 4 input matrix.m00 m01 m02 m03m10 m11 m12 m13m20 m21 m22 m23m30 m31 m32 m33Basic Input/Output:Input 1: 6 7 3 4 8 9 2 1 1 2 9 6 6 5 7 2Out 4 min read Java Program to Interchange Elements of First and Last in a Matrix Across RowsFor a given 4 × 4 matrix, the task is to interchange the elements of the first and last rows and then return the resultant matrix. Illustration: Input 1: 1 1 5 0 2 3 7 2 8 9 1 3 6 7 8 2 Output 1: 6 7 8 2 2 3 7 2 8 9 1 3 1 1 5 0 Input 2: 7 8 9 10 11 13 14 1 15 7 12 22 11 21 30 1 Output 2: 11 21 30 1 3 min read Java Program to Interchange Elements of First and Last in a Matrix Across ColumnsFor a given 4 x 4 matrix, the task is to interchange the elements of the first and last columns and then return the resultant matrix.Example Test Case for the ProblemInput : 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16Output : 4 2 3 1 8 6 7 5 12 10 11 9 16 14 15 13 Implementation of Interchange Elements o 2 min read Java String ProgramsJava Program to Get a Character from a StringGiven a String str, the task is to get a specific character from that String at a specific index. Examples:Input: str = "Geeks", index = 2Output: eInput: str = "GeeksForGeeks", index = 5Output: F Below are various ways to do so: Using String.charAt() method: Get the string and the indexGet the speci 5 min read Replace a character at a specific index in a String in JavaIn Java, here we are given a string, the task is to replace a character at a specific index in this string. Examples of Replacing Characters in a StringInput: String = "Geeks Gor Geeks", index = 6, ch = 'F'Output: "Geeks For Geeks."Input: String = "Geeks", index = 0, ch = 'g'Output: "geeks"Methods t 3 min read Reverse a String in JavaIn Java, reversing a string means reordering the string characters from the last to the first position. Reversing a string is a common task in many Java applications and can be achieved using different approaches. In this article, we will discuss multiple approaches to reverse a string in Java with 7 min read Java Program to Reverse a String using StackThe Stack is a linear data structure that follows the LIFO(Last In First Out) principle, i.e, the element inserted at the last is the element to come out first. Approach: Push the character one by one into the Stack of datatype character.Pop the character one by one from the Stack until the stack be 2 min read Sort a String in Java (2 different ways)The string class doesn't have any method that directly sorts a string, but we can sort a string by applying other methods one after another. The string is a sequence of characters. In java, objects of String are immutable which means a constant and cannot be changed once created. Creating a String T 6 min read Swapping Pairs of Characters in a String in JavaGiven string str, the task is to write a Java program to swap the pairs of characters of a string. If the string contains an odd number of characters then the last character remains as it is. Examples: Input: str = “Javaâ€Output: aJav Explanation: The given string contains even number of characters. 3 min read Check if a given string is Pangram in JavaGiven string str, the task is to write Java Program check whether the given string is a pangram or not. A string is a pangram string if it contains all the character of the alphabets ignoring the case of the alphabets. Examples: Input: str = "Abcdefghijklmnopqrstuvwxyz"Output: YesExplanation: The gi 3 min read Print first letter of each word in a string using regexGiven a string, extract the first letter of each word in it. "Words" are defined as contiguous strings of alphabetic characters i.e. any upper or lower case characters a-z or A-Z. Examples: Input : Geeks for geeksOutput :Gfg Input : United KingdomOutput : UKBelow is the Regular expression to extract 3 min read Java Program to Determine the Unicode Code Point at Given Index in StringASCII is a code that converts the English alphabets to numerics as numeric can convert to the assembly language which our computer understands. For that, we have assigned a number against each character ranging from 0 to 127. Alphabets are case-sensitive lowercase and uppercase are treated different 5 min read Remove Leading Zeros From String in JavaGiven a string of digits, remove leading zeros from it.Illustrations: Input : 00000123569Output: 123569Input: 000012356090Output: 12356090Approach: We use the StringBuffer class as Strings are immutable.Count leading zeros by iterating string using charAt(i) and checking for 0 at the "i" th indices. 3 min read Compare two Strings in JavaString in Java are immutable sequences of characters. Comparing strings is the most common task in different scenarios such as input validation or searching algorithms. In this article, we will learn multiple ways to compare two strings in Java with simple examples.Example:To compare two strings in 4 min read Compare two strings lexicographically in JavaIn this article, we will discuss how we can compare two strings lexicographically in Java. One solution is to use Java compareTo() method. The method compareTo() is used for comparing two strings lexicographically in Java. Each character of both the strings is converted into a Unicode value for comp 3 min read Java program to print Even length words in a StringGiven a string s, write a Java program to print all words with even length in the given string. Example to print even length words in a String Input: s = "i am Geeks for Geeks and a Geek" Output: am GeekExample:Java// Java program to print // even length words in a string class GfG { public static v 3 min read Insert a String into another String in JavaGiven a String, the task is to insert another string in between the given String at a particular specified index in Java. Examples: Input: originalString = "GeeksGeeks", stringToBeInserted = "For", index = 4 Output: "GeeksForGeeks" Input: originalString = "Computer Portal", stringToBeInserted = "Sci 4 min read Split a String into a Number of Substrings in JavaGiven a String, the task it to split the String into a number of substrings. A String in java can be of 0 or more characters. Examples : (a) "" is a String in java with 0 character (b) "d" is a String in java with 1 character (c) "This is a sentence." is a string with 19 characters. Substring: A Str 5 min read Article Tags : Java java-basics Practice Tags : Java Like