JAVA QUIZZ 1

What will be the output when executing this main?

public class Swap {
 public static void swapStrings(String x, String y){
  String temp = x;
  x=y;
  y=temp;
 }

 public static void main(String[] args) {
  String a = "1";
  String b = "2";
  swapStrings(a, b);
  System.out.println("a="+a+" ,b="+b);
 }
}

An exception will be thrown
“a=2 ,b=1”
“a=1 ,b=2” because strings are immutable
"a=1 ,b=2" because Java passes parameters by value (careful no return)

What happens with following program?

class Parent{
  protected void x(){}
  public void y(){}
}

public class Child extends Parent{
  public void x(){}
  protected void y(){}
}

It compiles successfully
Compilation error – x can’t have its visibility increased
Compilation error – y can not have its visibility reduced
Compilation error – neither x nor y can have their visibility changed

Following code will result in:

int a = 3.5;

Compilation error
Runtime error
A being 3.5
A being 3

Following code will result in:

int a1 = 5;
double a2 = (float) a1;

Compilation error
Runtime error
No errors : By default, Java uses double to represent its floating-point numerals. float is 32 bits whereas double is 64

Following code will give:

class A {
    int b = 1;

    public static void main(String[] args) {
        System.out.println("b is " + b);
    }
}

Compilation error (non static field cannot be referenced from a static context)
Runtime Error
Runtime Exception
b is 1

Following code will result in:

class A {
    public static void main(String[] args) {
        B b = new A();
    }
}

class B extends A {
}

Compile error
Runtime Exception
No error

Following code will result in:

class A {
    public static void main(String[] args) {
        A a = new B();
    }
}

class B extends A {
}

Compiler error
Runtime Exception
No error

Methods that are marked protected can be called in any subclass of that class

True
False

Can you compare a boolean to an integer?

True
False

An abstract class can have non-abstract methods.

True
False

What is an instanceof

A method in object
An operator and keyword

If class A implements an interface does it need to implement all methods of that interface?

Yes, always
No, not when A is abstract

Which JDBC method is used to execute INSERT, DELETE, UPDATE , and other SQL DDL such as CREATE, DROP TABLE.

executeUpdate()
executeQuery()
execute()

Which JDBC method is used for retrieving a string value (SQL type VARCHAR) and assigning into java String object.

getVarchar()
getObject()
getString()

This method is used for retrieving the value from current row as object.

getRow()
getObject()
getString()

What happens when you do if (a==b)?

Integer a = new Integer(2);
Integer b = new Integer(2);

Compiler error
Runtime Exception
True
False

Synchronized is a keyword to tell a Thread to grab an Object lock before continuing execution.

True
False

Which ones does not extend java.lang.Number ? (you can make multiple choices)

Which JDBC method is used to execute any SQL statement with a "SELECT" clause, that return the result of the query as a result set.

ExecuteUpdate()
ExecuteQuery()
Execute()

Which JDBC method is used to execute INSERT, DELETE, UPDATE , and other SQL DDL such as CREATE, DROP TABLE.

ExecuteUpdate()
ExecuteQuery()
Execute()

Which JDBC method is used for retrieving a string value (SQL type VARCHAR) and assigning into java String object.

GetVarchar()
GetObject()
GetString()

This method is used for retrieving the value from current row as object.

GetRow()
GetObject()
GetString()

The Connection.prepareStatement() method accepts a SQL query and returns a...

PreparedStatement object
CallableStatement object
PrepareCall method

This method returns an integer value indicating a row count.

executeQuery()
executeUpdate()
execute()

Consider the following class

public class Test implements Runnable{
    public void run() {
    }
}

Creating an instance of this class and calling its run() method will spawn a new thread:

True
False

An application that creates an instance of Thread must provide the code that will run in that thread. There are two ways to do this:

Provide a Runnable object. The Runnable interface defines a single method, run, meant to contain the code executed in the thread. The Runnable object is passed to the Thread constructor, as in the HelloRunnable example:

public class HelloRunnable implements Runnable {
    public void run() {
        System.out.println("Hello from a thread!");
    }

    public static void main(String args[]) {
        (new Thread(new HelloRunnable())).start();
    }
}

Subclass Thread. The Thread class itself implements Runnable, though its run method does nothing. An application can subclass Thread, providing its own implementation of run, as in the HelloThread example:

public class HelloThread extends Thread {
    public void run() {
        System.out.println("Hello from a thread!");
    }

    public static void main(String args[]) {
        (new HelloThread()).start();
    }
}

What is the result of attempting to compile and run the following code?

public class Test {
    public static void main(String[] args){
        Integer a = new Integer(4);
        Integer b = new Integer(8);
        Set hs = new HashSet();
        hs.add(a);
        hs.add(b);
        hs.add(a);
        System.out.println(hs.size());
    }
}

It prints: 2
It prints: 3

What is the result of attempting to compile and run the following code?

public class Test {
    public static void main(String[] args){
        Integer a = new Integer(4);
        Integer b = new Integer(8);
        Integer c = new Integer(4);
        Set hs = new HashSet();
        hs.add(a);
        hs.add(b);
        hs.add(c);
        System.out.println(hs.size());
    }
}

It prints: 2
It prints: 3

What will this program print out?

class Figure {
    public void print() {
        System.out.println("FIGURE");
    }
}

class Triangle extends Figure {
    public void print() {
        System.out.println("TRIANGLE");
    }
}

public class Test {
    public static void main(String[] args) {
        Figure f1 = new Figure();
        f1.print();
        Figure f2 = new Triangle();
        f2.print();
        Triangle t = new Triangle();
        t.print();
    }
}

FIGURE FIGURE FIGURE
FIGURE FIGURE TRIANGLE
FIGURE TRIANGLE TRIANGLE