Interface java Example Interview

 //interface Only public, static and final are allowed.

//No. Interfaces can’t have constructors.
interface Test{

    static  int s=2;
    final int d=4;
    void get();
    int getmultiple();

}


// initializers not allowed in interfaces
/*interface demoStatic(){
    {  System.out.println("empty implemented");}
    
    static{
         System.out.println("static implemented"); 
    }
}*/


interface B{
    int getdivide(int i);
    //  int getadd();//implementation is required in Class A
}

class A implements B{

    public int getdivide(int i ){
        return  i*i;
    }
}


class p{

    interface Q{
        int i=111;
    }
}

interface NextTest extends Test{
    int t=5;
    void get();

    int getadd();

    //  int getValue();//Demo is not abstract and does not override abstract method getValue() in NextTest
}

class Demo implements Test, NextTest {

    public int getadd(){
        return d+t;
    }

    public int getmultiple(){
        return d*t;
    }
    public void get(){
        System.out.println("demo get method implemented");
    }


}
class XDemo extends Demo{

}

/*class XXDemo implements NextTest{
    void methodD(){
        i=4;
        //No, because interface fields are static and 
        //final by default and you can’t change
        //their value once they are initialized. In the above code, methodB() 
        //is changing value of interface field A.i. It shows compile time error.
    }
}*/


public class MyClass {
    public static void main(String args[]) {

        System.out.println("Interface");

        Test s=new XDemo();
        s.get();
        //  System.out.println("sum : "+ s.getadd());//it will check in Test interface error not found

        System.out.println("multiple : "+ s.getmultiple());
        NextTest st=new XDemo();
        System.out.println("add : "+ st.getadd());

        // XDemo s=new NextTest();//NextTest is abstract; cannot be instantiated
        XDemo sp=new XDemo();
        System.out.println("addd : "+ sp.getadd());
        System.out.println("multiple : "+ sp.getmultiple());



        B newS=new A();

        System.out.println("divide : "+ newS.getdivide(12));
        // p ps=new Q();
        B bs=new B(){
            public int getdivide(int i){
                return i*i;          }

        };

        System.out.println("divide : "+  bs.getdivide(12));
    }
}

Find the character element which appears maximum number of times in an String

 //Find the element which appears maximum number of times in an array

import java.util.Arrays;
public class MyClass {
    public static void main(String args[]) {

        String name="amitrawat";

        char[] word=name.toCharArray();

        for(int i=0;i<word.length;i++){

            for(int j=i+1;j<word.length;j++){
                char first=word[i];
                char second=word[j];
                char temp;

                if(first>second){
                    temp=first;
                    word[i]=second;
                    word[j]=temp;
                }
            }

        }

        System.out.println("max number : " +  String.valueOf(word));


        //getting max character and times
        char maxchar=word[0];
        int times=0;
        for(int i=0;i<word.length;i++){

            char w=word[i];

            if(maxchar==w){
                times++;

            }else if(maxchar<w){
                times=1;
                maxchar=w;

            }
        }

        System.out.println("char max  : " + maxchar);
        System.out.println("char times: " + times);
    }
}

OUTPUT

max number : aaaimrttw
char max  : w
char times: 1

Find the element which appears maximum number of times in an array

import java.util.Arrays;
public class MyClass {
    public static void main(String args[]) {
        int max = 0, count = 0;
        int[] a={1,2,3,4,8,8,9,8,3,3,5,3,4,5,6,8};

        //sorting array   
        for(int i=0;i<a.length;i++){

            for(int j=i+1;j<a.length;j++){
                int first=a[i];
                int second=a[j];
                int temp=0;

                if(first>second){

                    temp=first;
                    a[i]=second;
                    a[j]=temp;

                }
            }
        }
        //  Arrays.sort(a);
        //finding highest number with times
        for(int i=0;i<a.length;i++){
            int num=a[i];

            if(max==num){
                count++;
            }else if(max<num){
                max=num;
                count=1;

            }
        }

        System.out.println("max number : " + max);
        System.out.println("times: " + count);
        
    }
}

OUTPUT

max number : 9
times: 1

Overloading and overriding Interview Example Code

 class Test {

    static int s = 4;
    final int d = 5;

    static void sit() {
        System.out.println(" sit method of  test class ");
    }

    void get() {
        System.out.println("  get method test class");

    }
}

class Test1 extends Test {
    static int s = 6;
    static int a = 2;
    final int d = 3;

    static void sit() {
        System.out.println("sit  method test1 class");
    }

    void get() {

        System.out.println("get  method get test1 class");
    }
}

class Test2 extends Test1 {
    static int s = 7;

    static void sit() {
        System.out.println("sit method test2 class");
    }

    void get() {
        System.out.println("get  method get test2 class");
    }

}

class Demo {
}

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("1 : test2 class instance of test2 class.......... ");
        System.out.println();
        Test2 obj2 = new Test2();
        //class c inherit static 
        System.out.println("static varialble : " + obj2.a); // 2
        System.out.println();

        System.out.println("final varibale : " + obj2.d); //3
        System.out.println();

        obj2.sit();//print method of test2 class 

        System.out.println();
        System.out.println();

        System.out.println("2 : test1 class instance of test2 class.......... ");
        System.out.println();
        Test1 obj1 = new Test2();

        obj1.sit();// print method of class test1 : static method
        System.out.println();


        obj1.get();//print method of class test2 :non static method
        System.out.println();


        //testing the type cast 
        Test objtrail1 = new Test1();//correct
        Test objtrail2 = new Test2();//correct

        // Test1 cannot be converted to Test2
        //     Test2 objtrail3=new Test1();//incorrect type cast error 

        // incompatible types: Test cannot be converted to Test2
        //    Test2 objtrail3=new Test();//incorrect type cast error


        //    Test1 obje=new Test();//error: incompatible types: Test cannot be converted to Test1

        System.out.println();
        System.out.println();
        System.out.println("3 : test class instance of test1 class.......... ");

        Test obje = new Test1();//the instance of test1 but print the static and final variable and static method of test
        System.out.println();

        System.out.println("print the static  variable of test class  " + obje.s);//4
        System.out.println();

        System.out.println("print the final  variable of test  class " + obje.d);//5
        System.out.println();

        obje.sit();//print the method of static test class 
        System.out.println();

        obje.get();//print method of non static test1 class

        System.out.println();


        //    System.out.println("3 : test2 class instance of test class.......... "); 


        // Test2 objet=new Test();

        // objet.sit();//error: incompatible types: Test cannot be converted to Test2
        //    Test2 objet=new Test1();//error: incompatible types: Test1 cannot be converted to Test2


        //    Test s=new Demo();//error: incompatible types: Demo cannot be converted to Test
    }
}

output :  

1 : test2 class instance of test2 class.......... 

static varialble : 2

final varibale : 3

sit method test2 class


2 : test1 class instance of test2 class.......... 

sit  method test1 class

get  method get test2 class



3 : test class instance of test1 class.......... 

print the static  variable of test class  4

print the final  variable of test  class 5

 sit method of  test class 

get  method get test1 class