switch case in Java - Quiz

Let's analyze the given expression and the output of the Java Math functions:

Expression:

Math.pow(36, 0.5) + Math.cbrt(125) + Math.ceil(4.2) + Math.floor(7.9)
        

Explanation:

1. Math.pow(36, 0.5):

   The Math.pow(x, y) method returns x raised to the power of y.
   Math.pow(36, 0.5) calculates the square root of 36.
   √36 = 6.0

2. Math.cbrt(125):

   The Math.cbrt(x) method returns the cube root of x.
   Math.cbrt(125) calculates the cube root of 125.
   ∛125 = 5.0

3. Math.ceil(4.2):

   The Math.ceil(x) method returns the smallest integer greater than or equal to x.
   Math.ceil(4.2) returns the smallest integer greater than or equal to 4.2.
   Math.ceil(4.2) = 5.0

4. Math.floor(7.9):

   The Math.floor(x) method returns the largest integer less than or equal to x.
   Math.floor(7.9) returns the largest integer less than or equal to 7.9.
   Math.floor(7.9) = 7.0

Calculating the Sum:

Adding these values together:
6.0 + 5.0 + 5.0 + 7.0 = 23.0

Conclusion:

The output of the expression is: 23.0

The this keyword in Java is used for a specific purpose related to the current instance of a class. Here's what each option means in the context of the this keyword:

a) It is used to declare a constant variable.

• This is incorrect. The this keyword is not used to declare constant variables. Constant variables in Java are declared using the final keyword.

b) It refers to the current instance of the class.

• This is correct. The this keyword is used to refer to the current instance of the class within its methods and constructors. It helps to distinguish between instance variables and parameters with the same name, and to call other constructors or methods within the same class.

c) It is used to call static methods.

• This is incorrect. Static methods can be called using the class name, not the this keyword. The this keyword cannot be used to call static methods.

d) It represents the return value of a function.

• This is incorrect. The return value of a function is specified using the return keyword, not this.

Correct Answer:

b) It refers to the current instance of the class.

Let's analyze the given Java code step by step to predict its output:

Code:

String str1 = "great";
String str2 = "minds";

System.out.println(str1.substring(0, 2).concat(str2.substring(1)));
System.out.println("WH" + (str1.substring(2).toUpperCase()));
        

Explanation:

1. First Line:

   System.out.println(str1.substring(0, 2).concat(str2.substring(1)));\
   - str1.substring(0, 2) extracts a substring from str1 starting at index 0 up to, but not including, index 2.
   For str1 = "great", str1.substring(0, 2) results in "gr".
   - str2.substring(1) extracts a substring from str2 starting at index 1 to the end of the string.
   For str2 = "minds", str2.substring(1) results in "inds".
   - Concatenating these results:
   "gr".concat("inds") results in "grinds".
   - Therefore, the first println statement prints "grinds".

2. Second Line:

   System.out.println("WH" + (str1.substring(2).toUpperCase()));
   - str1.substring(2) extracts a substring from str1 starting at index 2 to the end of the string.
   For str1 = "great", str1.substring(2) results in "eat".
   - str1.substring(2).toUpperCase() converts this substring to uppercase.
   "eat".toUpperCase() results in "EAT".
   - Concatenating "WH" with the result:
   "WH" + "EAT" results in "WHEAT".
   - Therefore, the second println statement prints "WHEAT".

Conclusion:

The output of the code is:

• grinds
• WHEAT

Let's analyze the given Java code step by step to determine its output:

Code:

char ch;
int x = 97;

do {
    ch = (char) x;
    System.out.print(ch + " ");
    if (x % 10 == 0)
        break;
    ++x;
} while (x <= 100);
        

Explanation:

1. Initialization:

   - x starts at 97.
   - In ASCII, 97 corresponds to the character 'a'.

2. Loop Execution:

   First Iteration:
   - ch = (char) x converts x to the character 'a'.
   - System.out.print(ch + " "); prints 'a'.
   - x % 10 for 97 is 7 (not zero), so the break statement is not executed.
   - ++x increments x to 98.

   Second Iteration:
   - ch = (char) x converts x to the character 'b'.
   - System.out.print(ch + " "); prints 'b'.
   - x % 10 for 98 is 8 (not zero), so the break statement is not executed.
   - ++x increments x to 99.

   Third Iteration:
   - ch = (char) x converts x to the character 'c'.
   - System.out.print(ch + " "); prints 'c'.
   - x % 10 for 99 is 9 (not zero), so the break statement is not executed.
   - ++x increments x to 100.

   Fourth Iteration:
   - ch = (char) x converts x to the character 'd'.
   - System.out.print(ch + " "); prints 'd'.
   - x % 10 for 100 is 0, so the break statement is executed, terminating the loop.

Conclusion:

The final output of the code is:

• a
• b
• c
• d

Let's analyze the given Java code segment to determine its output:

Code:

int i;
for (i = 5; i > 10; i++)
    System.out.println(i);

System.out.println(1 * 4);
        

Explanation:

1. For Loop Analysis:

   for (i = 5; i > 10; i++):
   - **Initialization:** i is initialized to 5.
   - **Condition:** The loop runs while i > 10.
   - **Update:** i is incremented by 1 after each iteration.
   Since i starts at 5 and 5 is not greater than 10, the loop condition is false from the beginning. Therefore, the loop body does not execute even once.

2. Next Line of Code:

   System.out.println(1 * 4);:
   - This statement prints the result of the expression 1 * 4, which is 4.

Conclusion:

The program does not produce an error, run infinitely, or run 5 times. The output of the program is:

• 4

Automatic conversion of primitive data into an object of a wrapper class is called autoboxing.

Explanation:

• Autoboxing is a feature in Java that allows automatic conversion between primitive types (such as int, float, double, etc.) and their corresponding wrapper classes (such as Integer, Float, Double, etc.).
• For example, Java automatically converts an int to an Integer when it is assigned to an Integer object or used in a context where an Integer is expected.

Correct Answer:

a) autoboxing

The parseLong() function is a member of the Long wrapper class.

Explanation:

• parseLong() is a static method provided by the Long wrapper class in Java.
• It is used to convert a String into a long value.

Correct Answer:

a) Long wrapper class

The method used to extract a single character from a String object in Java is charAt().

Explanation:

• charAt(int index) is a method of the String class that returns the character at the specified index in the string. The index is zero-based, meaning the first character is at index 0.

Correct Answer:

c) charAt()

Invoking a method by passing the object of a class is known as call by reference.

Explanation:

• Call by Reference: When you pass an object to a method, you are passing a reference to that object, not a copy of the object itself. Thus, changes made to the object inside the method affect the original object.

• Call by Value: This means passing a copy of the value of the variable. In Java, primitive types are passed by value, but objects are passed by reference.

Correct Answer:

b) Call by reference

To stop the execution of a construct, such as a loop or a switch statement, the correct statement is:

b) break

Explanation:

• break: This statement is used to exit from a loop (like for, while, or do-while) or a switch statement. When break is encountered, the execution of the loop or switch construct is immediately terminated.

• System.exit(0): This terminates the entire Java Virtual Machine (JVM), not just a single construct.

• stop: This is not a valid Java statement for stopping execution.

• end: This is not a valid Java statement for stopping execution.

Correct Answer:

b) break