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Java Quiz

1.

Which of the following is not an inbuilt package?

2.

Which of the Exception is thrown when the following code is run?

public class Sample {
    public static void main(String[] args) {
        String[] names = new String[3];
        names[0] = "Sherlock";
        names[1] = "Watson";
        names[2] = "Mary";
        System.out.println(names[4]);
    }
}

Explaination

ArrayIndexOutOfBoundsException occurs when an element is accessed with an index greater than the size of array.

3.

Which of the following code can be used to add two integers?

4.

Which is the final state in an Object Life-cycle?

Explaination

Java Object Life-cycle:

1. Created
2. In use (strongly reachable)
3. Invisible
4. Unreachable
5. Collected
6. Finalized
7. Deallocated

5.

What is the output of the following code.

public class Sample {

	public static void main(String[] args) {
		System.out.println(5 & 9);
	}

}

Explaination

& is bitwise operator. 5 & 9 = 00000101 & 00001001 = 00000001 = 1.

6.

Is 'String[] args' mandatory in the definition of main method?

Explaination

Its an architecture decision taken by Java Designers.

7.

Which of the following is a valid keyword

Explaination

Java is statistically typed programming language. string is different from String. In Java we have String class, but no string. Similarly FLOAT and Try. throw is a valid keyword. throw is the keyword used to throw exceptions to the calling method.

8.

What could be the output of following program?

import java.util.ArrayList;

public class Sample {
	
	public static void main(String[] args) {
		ArrayList numbers = new ArrayList();
		numbers.add(1);
		numbers.add(2);
		numbers.add(3);
		
		int sum = 0;
		
		numbers.forEach(number ->{
			sum = sum + number;
		});
		
		System.out.println(sum);
		
	}
}

Explaination

Compile Error:
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
Local variable sum defined in an enclosing scope must be final or effectively final

9.

Can constructor return a value?

Explaination

Constructor can never return a value. A constructor is called by the memory allocation and object initialization code in the Java Runtime. A user code should never expect a return value from constructor.

10.

In the following program, code block 1 runs fine while code block 2 throws NullPointerException. Why?

public class Sample {
	
	public static void main(String[] args) {
		String s = null;
		
		// code block 1
		if(s != null && s.length() < 10) {
			System.out.println("");
		} else {
			System.out.println("s is null");
		}
		
		// code block 2
		if(s.length()>10) {
			System.out.println("s have length > 10");
		}
		
	}
}

Explaination

When using the conditional and and or operators (&& and ||), Java does not evaluate the second operand unless it is necessary to resolve the result. This allows statements like if (s != null && s.length() < 10) to work reliably. This is called Short Circuiting.

11.

Which of the following is preferred while programming with Threads

Explaination

StringBuffer is thread safe.

12.

Method Overloading is an example of

Explaination

Which method would be called is determined by the parameter list at the compile time. Resolving the methods to be called at Compile time is called Static Binding and while at runtime, is called Dynamic Binding.

13.

What is the value of i that is printed?

public class Sample {
	
	public static void main(String[] args) {
		int i;
		System.out.println(i);
	}
}

Explaination

Compile Error occurs with the following message:
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
The local variable i may not have been initialized

14.

What could be the output of the following program.

class Main {
	public static void main(String args[]) {   
		System.out.println(getNum());
	} 
	
	public int getNum() {
		return 12;
	}
}

Explaination

Java does not allow to call a non-static method from a static method without object reference.

15.

What is the output of following program?

public class Sample {
	
	public static void main(String[] args) {
		if(2) {
			System.out.println("true");
		} else {
			System.out.println("false");
		}
		
	}
}

Explaination

Compile Error with the message "Type mismatch: cannot convert from int to boolean".

16.

What is the output of the following program:

public class Main {
	
	public static void main(String[] args) {
		int sum = 0;
		for(int i=0;i<10;i++) {
			sum = i;
		}
		System.out.println(sum);
	}
}

Explaination

Each time in the loop, sum is loaded with i value. The last time the loop is executed, i has a value of 9. Therefore sum=9 and 9 is printed to the console.

17.

Method Overriding is an example of

Explaination

It is only during runtime, the method specific to the object is run. Hence dynamic.

18.

Which of the following is not a builtin datatype?

Explaination

Java Builtin Datatypes are: boolean, byte, char, short, int, long, float, double.

19.

Which of the following operator cannot be applied for integer operands?

Explaination

&& accepts only boolean values are operands. If && is applied on two integer operands, compilation error with the message \"The operator && is undefined for the argument type(s) int, int\" would be displayed.

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