1. Analyze the following code:
public class Test extends A {
public static void main(String[] args) {
Test t = new Test();
t.print();
}
}
class A {
String s;
A(String s) {
this.s = s;
}
public void print() {
System.out.println(s);
}
}
1. The program would compile if a default constructor A(){ } is added to class A explicitly.
2. The program has an implicit default constructor Test(), but it cannot be compiled, because its super class does not have a default constructor. The program would compile if the constructor in the class A were removed.
2. What is the output of running class C?
class A {
public A() {
System.out.println(
“The default constructor of A is invoked”);
}
}
class B extends A {
public B() {
System.out.println(
“The default constructor of B is invoked”);
}
}
public class C {
public static void main(String[] args) {
B b = new B();
}
}
“The default constructor of A is invoked” followed by “The default constructor of B is invoked”
3). Analyze the following code:
public class Test {
public static void main(String[] args) {
B b = new B();
b.m(5);
System.out.println(“i is ” + b.i);
}
}
class A {
int i;
public void m(int i) {
this.i = i;
}
}
class B extends A {
public void m(String s) {
}
}
The method m is not overridden in B. B inherits the method m from A and defines an overloaded method m in B.
4. What is the output of the following code?
public class Test {
public static void main(String[] args) {
new Person().printPerson();
new Student().printPerson();
}
}
class Student extends Person {
@Override
public String getInfo() {
return “Student”;
}
}
class Person {
public String getInfo() {
return “Person”;
}
public void printPerson() {
System.out.println(getInfo());
}
}
Person Student
5. Given two reference variables t1 and t2, if t1 == t2 is true, t1.equals(t2) must be ________.
true
6. Analyze the following code
public class Test {
public static void main(String[] args) {
Object a1 = new A();
Object a2 = new A();
System.out.println(a1.equals(a2));
}
}
class A {
int x;
public boolean equals(A a) {
return this.x == a.x;
}
}
// Program 2:
public class Test {
public static void main(String[] args) {
A a1 = new A();
A a2 = new A();
System.out.println(a1.equals(a2));
}
}
class A {
int x;
public boolean equals(A a) {
return this.x == a.x;
}
}
Program 1 displays false and Program 2 displays true.
7. For the questions below, consider the following class definition:
public class AClass
{
Redefine addEm to return the value of z + super.addEmegg, but leave changeEm alone
8). For the questions below, use the following partial class definitions:
public class A1
{
x, z, a, b
9. If class AParentClass has a protected instance data x, and AChildClass is a derived class of AParentClass, then AChildClass can access x but can not redefine x to be a different type.
False
10. If classes C1 and C2 both implement an interface Cint, which has a method whichIsIt, and if C1 c = new C1 ; is performed at one point of the program, then a later instruction c.whichIsIt ; will invoke the whichIsIt method defined in C1.
False
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