In this tutorial, we will learn about Java interfaces. We will learn how to implement interfaces and when to use them in detail with the help of examples.<\/p>\n\n\n\n
An interface is a fully abstract class. It includes a group of abstract methods (methods without a body).<\/p>\n\n\n\n
We use the Here,<\/p>\n\n\n\n Like abstract classes, we cannot create objects of interfaces.<\/p>\n\n\n\n To use an interface, other classes must implement it. We use the Output<\/strong><\/p>\n\n\n\n In the above example, we have created an interface named Polygon<\/var>. The interface contains an abstract method Here, the Rectangle<\/var> class implements Polygon<\/var>. And, provides the implementation of the Output<\/strong><\/p>\n\n\n\n In the above example, we have created an interface named Language<\/var>. The interface includes an abstract method Here, the ProgrammingLanguage<\/var> class implements the interface and provides the implementation for the method.<\/p>\n\n\n\n In Java, a class can also implement multiple interfaces. For example,<\/p>\n\n\n\n Similar to classes, interfaces can extend other interfaces. The Here, the Polygon<\/var> interface extends the Line<\/var> interface. Now, if any class implements Polygon<\/var>, it should provide implementations for all the abstract methods of both Line<\/var> and Polygon<\/var>.<\/p>\n\n\n\n An interface can extend multiple interfaces. For example,<\/p>\n\n\n\n Now that we know what interfaces are, let’s learn about why interfaces are used in Java.<\/p>\n\n\n\n Note<\/strong>: All the methods inside an interface are implicitly With the release of Java 8, we can now add methods with implementation inside an interface. These methods are called default methods.<\/p>\n\n\n\n To declare default methods inside interfaces, we use the Let’s take a scenario to understand why default methods are introduced in Java.<\/p>\n\n\n\n Suppose, we need to add a new method in an interface.<\/p>\n\n\n\n We can add the method in our interface easily without implementation. However, that’s not the end of the story. All our classes that implement that interface must provide an implementation for the method.<\/p>\n\n\n\n If a large number of classes were implementing this interface, we need to track all these classes and make changes to them. This is not only tedious but error-prone as well.<\/p>\n\n\n\n To resolve this, Java introduced default methods. Default methods are inherited like ordinary methods.<\/p>\n\n\n\n Let’s take an example to have a better understanding of default methods.<\/p>\n\n\n\n Output<\/strong><\/p>\n\n\n\n In the above example, we have created an interface named Polygon<\/var>. It has a default method Here, we have created two classes Rectangle<\/var> and Square<\/var> that implement Polygon<\/var>.<\/p>\n\n\n\n The Rectangle<\/var> class provides the implementation of the Now, while calling the The Java 8 also added another feature to include static methods inside an interface.<\/p>\n\n\n\n Similar to a class, we can access static methods of an interface using its references. For example,<\/p>\n\n\n\n Note<\/strong>: With the release of Java 9, private methods are also supported in interfaces.<\/p>\n\n\n\n We cannot create objects of an interface. Hence, private methods are used as helper methods that provide support to other methods in interfaces.<\/p>\n\n\n\n Let’s see a more practical example of Java Interface.<\/p>\n\n\n\n Output<\/strong><\/p>\n\n\n\n In the above program, we have created an interface named Polygon<\/var>. It includes a default method We can calculate the perimeter of all polygons in the same manner so we implemented the body of Now, all polygons that implement Polygon<\/var> can use However, the rule for calculating the area is different for different polygons. Hence, Any class that implements Polygon<\/var> must provide an implementation of In this tutorial, we will learn about Java interfaces. We will learn how to implement interfaces and when to use them in detail with the help of examples. An interface is a fully abstract class. It includes a group of abstract methods (methods without a body). We use the interface keyword to create an interface in Java. […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[531],"tags":[],"_links":{"self":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/1210"}],"collection":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/comments?post=1210"}],"version-history":[{"count":0,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/1210\/revisions"}],"wp:attachment":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/media?parent=1210"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/categories?post=1210"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/tags?post=1210"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}interface<\/code> keyword to create an interface in Java. For example,<\/p>\n\n\n\ninterface Language {\n public void getType();\n\n public void getVersion();\n}<\/code><\/pre>\n\n\n\ngetType()<\/code> and getVersion()<\/code>.<\/li><\/ul>\n\n\n\n
\n\n\n\nImplementing an Interface<\/h2>\n\n\n\n
implements<\/code> keyword to implement an interface.<\/p>\n\n\n\nExample 1: Java Interface<\/h3>\n\n\n\n
interface Polygon {\n void getArea(int length, int breadth);\n}\n\n\/\/ implement the Polygon interface\nclass Rectangle implements Polygon {\n\n \/\/ implementation of abstract method\n public void getArea(int length, int breadth) {\n System.out.println(\"The area of the rectangle is \" + (length * breadth));\n }\n}\n\nclass Main {\n public static void main(String[] args) {\n Rectangle r1 = new Rectangle();\n r1.getArea(5, 6);\n }\n}<\/code><\/pre>\n\n\n\nThe area of the rectangle is 30<\/samp><\/code><\/pre>\n\n\n\ngetArea()<\/code>.<\/p>\n\n\n\ngetArea()<\/code> method.<\/p>\n\n\n\n
\n\n\n\nExample 2: Java Interface<\/h3>\n\n\n\n
\/\/ create an interface\ninterface Language {\n void getName(String name);\n}\n\n\/\/ class implements interface\nclass ProgrammingLanguage implements Language {\n\n \/\/ implementation of abstract method\n public void getName(String name) {\n System.out.println(\"Programming Language: \" + name);\n }\n}\n\nclass Main {\n public static void main(String[] args) {\n ProgrammingLanguage language = new ProgrammingLanguage();\n language.getName(\"Java\");\n }\n}<\/code><\/pre>\n\n\n\nProgramming Language: Java<\/samp><\/code><\/pre>\n\n\n\ngetName()<\/code>.<\/p>\n\n\n\n
\n\n\n\nImplementing Multiple Interfaces<\/h3>\n\n\n\n
interface A {\n \/\/ members of A\n}\n\ninterface B {\n \/\/ members of B\n}\n\nclass C implements A, B {\n \/\/ abstract members of A\n \/\/ abstract members of B\n}<\/code><\/pre>\n\n\n\n
\n\n\n\nExtending an Interface<\/h2>\n\n\n\n
extends<\/code> keyword is used for extending interfaces. For example,<\/p>\n\n\n\ninterface Line {\n \/\/ members of Line interface\n}\n\n\/\/ extending interface\ninterface Polygon extends Line {\n \/\/ members of Polygon interface\n \/\/ members of Line interface\n}<\/code><\/pre>\n\n\n\n
\n\n\n\nExtending Multiple Interfaces<\/h3>\n\n\n\n
interface A {\n ...\n}\ninterface B {\n ... \n}\n\ninterface C extends A, B {\n ...\n}<\/code><\/pre>\n\n\n\n
\n\n\n\nAdvantages of Interface in Java<\/h2>\n\n\n\n
Here, we know getArea()<\/code> calculates the area of polygons but the way area is calculated is different for different polygons. Hence, the implementation of getArea()<\/code> is independent of one another.<\/li>
In our previous example, we have used getArea()<\/code> as a specification inside the interface Polygon<\/var>. This is like setting a rule that we should be able to get the area of every polygon.
Now any class that implements the Polygon<\/var> interface must provide an implementation for the getArea()<\/code> method.<\/li>
interface Line { \u2026 } interface Polygon { \u2026 } class Rectangle implements Line, Polygon { \u2026 }<\/code>
Here, the class Rectangle<\/var> is implementing two different interfaces. This is how we achieve multiple inheritance in Java.<\/li><\/ul>\n\n\n\npublic<\/code> and all fields are implicitly public static final<\/code>. For example,<\/p>\n\n\n\ninterface Language {\n \n \/\/ by default public static final\n String type = \"programming language\";\n\n \/\/ by default public\n void getName();\n}<\/code><\/pre>\n\n\n\n
\n\n\n\ndefault methods in Java Interfaces<\/h2>\n\n\n\n
default<\/code> keyword. For example,<\/p>\n\n\n\npublic default void getSides() {\n \/\/ body of getSides()\n}<\/code><\/pre>\n\n\n\nWhy default methods?<\/h3>\n\n\n\n
\n\n\n\nExample: Default Method in Java Interface<\/h3>\n\n\n\n
interface Polygon {\n void getArea();\n\n \/\/ default method \n default void getSides() {\n System.out.println(\"I can get sides of a polygon.\");\n }\n}\n\n\/\/ implements the interface\nclass Rectangle implements Polygon {\n public void getArea() {\n int length = 6;\n int breadth = 5;\n int area = length * breadth;\n System.out.println(\"The area of the rectangle is \" + area);\n }\n\n \/\/ overrides the getSides()\n public void getSides() {\n System.out.println(\"I have 4 sides.\");\n }\n}\n\n\/\/ implements the interface\nclass Square implements Polygon {\n public void getArea() {\n int length = 5;\n int area = length * length;\n System.out.println(\"The area of the square is \" + area);\n }\n}\n\nclass Main {\n public static void main(String[] args) {\n\n \/\/ create an object of Rectangle\n Rectangle r1 = new Rectangle();\n r1.getArea();\n r1.getSides();\n\n \/\/ create an object of Square\n Square s1 = new Square();\n s1.getArea();\n s1.getSides();\n }\n}<\/code><\/pre>\n\n\n\nThe area of the rectangle is 30\nI have 4 sides.\nThe area of the square is 25\nI can get sides of a polygon.<\/samp><\/code><\/pre>\n\n\n\ngetSides()<\/code> and an abstract method getArea()<\/code>.<\/p>\n\n\n\ngetArea()<\/code> method and overrides the getSides()<\/code> method. However, the Square<\/var> class only provides the implementation of the getArea()<\/code> method.<\/p>\n\n\n\ngetSides()<\/code> method using the Rectangle<\/var> object, the overridden method is called. However, in the case of the Square<\/var> object, the default method is called.<\/p>\n\n\n\n
\n\n\n\nprivate and static Methods in Interface<\/h2>\n\n\n\n
\/\/ create an interface\ninterface Polygon {\n staticMethod(){..}\n}\n\n\/\/ access static method\nPolygon.staticMethod();<\/code><\/pre>\n\n\n\n
\n\n\n\nPractical Example of Interface<\/h3>\n\n\n\n
\/\/ To use the sqrt function\nimport java.lang.Math;\n\ninterface Polygon {\n void getArea();\n \n \/\/ calculate the perimeter of a Polygon\n default void getPerimeter(int... sides) {\n int perimeter = 0;\n for (int side: sides) {\n perimeter += side;\n }\n\n System.out.println(\"Perimeter: \" + perimeter);\n }\n}\n\nclass Triangle implements Polygon {\n private int a, b, c;\n private double s, area;\n\n\/\/ initializing sides of a triangle\n Triangle(int a, int b, int c) {\n this.a = a;\n this.b = b;\n this.c = c;\n s = 0;\n }\n\n\/\/ calculate the area of a triangle\n public void getArea() {\n s = (double) (a + b + c)\/2;\n area = Math.sqrt(s*(s-a)*(s-b)*(s-c));\n System.out.println(\"Area: \" + area);\n }\n}\n\nclass Main {\n public static void main(String[] args) {\n Triangle t1 = new Triangle(2, 3, 4);\n\n\/\/ calls the method of the Triangle class\n t1.getArea();\n\n\/\/ calls the method of Polygon\n t1.getPerimeter(2, 3, 4);\n }\n}<\/code><\/pre>\n\n\n\nArea: 2.9047375096555625\nPerimeter: 9<\/samp><\/code><\/pre>\n\n\n\ngetPerimeter()<\/code> and an abstract method getArea()<\/code>.<\/p>\n\n\n\ngetPerimeter()<\/code> in Polygon<\/var>.<\/p>\n\n\n\ngetPerimeter()<\/code> to calculate perimeter.<\/p>\n\n\n\ngetArea()<\/code> is included without implementation.<\/p>\n\n\n\ngetArea()<\/code>.<\/p>\n","protected":false},"excerpt":{"rendered":"