Java OOPs Concepts Test 1

Which of the following correctly creates an object of class Car?

class Car {}

What does Java provide if no constructor is defined in a class?

class Person {}

Which of the following is true about single inheritance in Java?

Which of the following demonstrates compile-time polymorphism in Java?

class Demo {
    void show() { System.out.println("No-arg"); }
    void show(int x) { System.out.println(x); }
}

Which of the following statements about abstract classes is true?

Which of the following statements is true about encapsulation?

Which of the following is true about interfaces in Java?

Which of the following is true about packages in Java?

Which of the following is true about a final variable in Java?

Which of the following is true about the Object class in Java?

What will be the output of the following code?

class Test {
    int x = 10;
}
public class Main {
    public static void main(String[] args) {
        Test t = new Test();
        System.out.println(t.x);
    }
}

Which statement correctly creates a parameterized constructor object?

class Car {
    String model;
    Car(String m) { model = m; }
}

What will be printed?

class A { void msg() { System.out.println("A"); } }
class B extends A { void msg() { System.out.println("B"); } }
class C extends B {}
public class Main {
    public static void main(String[] args) {
        C obj = new C();
        obj.msg();
    }
}

What will be printed?

class Demo {
    int add(int a, int b) { return a + b; }
    double add(double a, double b) { return a + b; }
}
public class Main {
    public static void main(String[] args) {
        Demo d = new Demo();
        System.out.println(d.add(5, 5));
        System.out.println(d.add(5.0, 5.0));
    }
}

What will happen when we run the following code?

abstract class A {
    abstract void show();
}
class B extends A {
    void show() { System.out.println("Hello"); }
}
public class Main {
    public static void main(String[] args) {
        A obj = new B();
        obj.show();
    }
}

What will be printed?

class Person {
    private String name;
    public void setName(String n) { name = n; }
    public String getName() { return name; }
}
public class Main {
    public static void main(String[] args) {
        Person p = new Person();
        p.setName("Alice");
        System.out.println(p.getName());
    }
}

What will be printed?

interface A { void show(); }
class B implements A { public void show() { System.out.println("Hello"); } }
public class Main {
    public static void main(String[] args) {
        A obj = new B();
        obj.show();
    }
}

Which statement is correct?

What will happen?

class Demo {
    final int x = 10;
    void change() {
        // x = 20;  // Uncommenting this line
    }
}

Which of the following methods are defined in Object class?