Java Fundamentals (D286)
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Free Java Fundamentals (D286) Questions
Which of the following best describes the primary functions of basic input and output (I/O) operations in Java?
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To perform mathematical calculations and manipulate data structures
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To read data from external sources and display results to the user
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To manage memory allocation and garbage collection
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To define classes and create objects
Explanation
Correct Answer
B. To read data from external sources and display results to the user
Explanation
Basic input and output (I/O) operations in Java are primarily concerned with reading data from external sources such as the keyboard, files, or network, and outputting results to destinations like the screen, files, or other devices. These operations are essential for interacting with users and external systems, enabling data communication and usability in applications.
Why other options are wrong
A. To perform mathematical calculations and manipulate data structures
This is incorrect because performing mathematical operations and manipulating data structures is handled through Java's core language features and libraries, not through its I/O operations. While these operations might be used in conjunction with I/O, they are not part of its primary function.
C. To manage memory allocation and garbage collection
This is wrong because memory management, including allocation and garbage collection, is handled automatically by the Java Virtual Machine (JVM), not through I/O operations. I/O operations are unrelated to how Java allocates memory or reclaims unused memory.
D. To define classes and create objects
This is incorrect because defining classes and creating objects is part of Java's object-oriented programming paradigm. It involves the use of classes, constructors, and the new keyword — not I/O operations. Basic I/O is instead concerned with external data input and output handling.
What is the effect of the ++ operator when applied before a variable in Java?
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Increments the variable after it's used
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Decrements the variable before it's used
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Increments the variable before it's used
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No effect
Explanation
Correct Answer
C. Increments the variable before it's used
Explanation
When the ++ operator is applied before a variable, it is known as the pre-increment operator. This operator increments the value of the variable before it is used in any expression. For example, if x = 5 and you write ++x, the value of x becomes 6 before it is used in the surrounding expression.
Why other options are wrong
A. Increments the variable after it's used
This is incorrect. This describes the post-increment operator (x++), where the variable is incremented after it is used in the expression.
B. Decrements the variable before it's used
This is incorrect. The -- operator is used for decrementing variables, not ++.
D. No effect
This is incorrect. The ++ operator does have an effect on the variable—it increments it by one.
What is a literal in Java?
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A reserved word
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A class in the API
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A value that represents a constant number or a constant String
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The return value of a method
Explanation
Correct Answer
C. A value that represents a constant number or a constant String
Explanation
In Java, a literal refers to a constant value that is directly represented in the code, such as a number, string, or character. For example, 5, "Hello", and 'A' are all literals in Java. These values are not variables and are directly used as fixed values in the program.
Why other options are wrong
A. A reserved word
This is incorrect. A reserved word (also known as a keyword) is a word that has a predefined meaning in Java, such as class, if, while, etc. Literals are values, not reserved words.
B. A class in the API
This is incorrect. While Java's standard library includes many classes in the API, a literal is not a class. A literal is a constant value directly represented in the code, not a class.
D. The return value of a method
This is incorrect. The return value of a method is a value that is returned from the method to the caller. While the return value could be a literal, it is not itself considered a literal. A literal is a fixed value directly used in code.
Which of the following represents the valid boolean literals in Java?
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0 and 1
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true and false
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yes and no
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on and off
Explanation
Correct Answer
B. true and false
Explanation
In Java, the valid boolean literals are true and false. These are used to represent the two possible values of a boolean type.
Why other options are wrong
A. 0 and 1
In Java, boolean values are not represented by 0 and 1; instead, they are represented by true and false.
C. yes and no
Java does not recognize yes and no as valid boolean literals.
D. on and off
Similarly, on and off are not valid boolean literals in Java. Only true and false are valid.
Which of the following statements is true about the static modifier?
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A static variable cannot change its value
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A static method is often written in non-Java language and exists outside of JVM
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A static method can access instance variables
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A static variable is shared by all the instances of the class
Explanation
Correct Answer
D. A static variable is shared by all the instances of the class
Explanation
A static variable is a class-level variable in Java, meaning it is shared among all instances of that class. Unlike instance variables that are tied to individual objects, static variables are stored in a common memory area and retain the same value across all instances unless explicitly changed. This feature is useful for representing common properties such as a counter or configuration shared by every object.
Why other options are wrong
A. A static variable cannot change its value
This is incorrect. A static variable can be modified unless it is also declared as final. The static keyword means it is shared, not immutable. Only final static variables are constants.
B. A static method is often written in non-Java language and exists outside of JVM
This is incorrect. Static methods are written in Java and exist within the JVM like all other methods. The concept of native methods (using the native keyword) refers to non-Java methods, not static ones.
C. A static method can access instance variables
This is incorrect because static methods belong to the class, not to any instance. They cannot directly access instance variables unless they are given an object reference to do so.
Which of the following statements accurately describes a decimal integer?
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A decimal integer is a number represented in base 2, using only 0s and 1s.
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A decimal integer is a number expressed in base 10, consisting of digits from 0 to 9.
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A decimal integer can include fractions and is represented in base 10.
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A decimal integer is a number that can only be negative.
Explanation
Correct Answer
B. A decimal integer is a number expressed in base 10, consisting of digits from 0 to 9.
Explanation
A decimal integer is a whole number that is expressed in base 10, the most common number system, which uses digits from 0 to 9. It does not include fractions or decimals.
Why other options are wrong
A. A decimal integer is a number represented in base 2, using only 0s and 1s.
This is incorrect because base 2 refers to binary numbers, not decimal integers. Binary uses only 0s and 1s.
C. A decimal integer can include fractions and is represented in base 10.
This is incorrect because a decimal integer refers only to whole numbers. Numbers that include fractions are not considered integers.
D. A decimal integer is a number that can only be negative.
This is incorrect because decimal integers can be both positive and negative. There's no restriction that they must be negative.
Out of the following claims, which is untrue?
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Java has two floating-point data types.
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The following declaration and assignment generates an error: float w = 1.2;
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1.0 is a long literal.
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Java has four floating-point data types.
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3.14 is a floating-point number.
Explanation
Correct Answer
C. 1.0 is a long literal.
Explanation
In Java, the number 1.0 is a double literal, not a long literal. Java treats floating-point numbers with decimal points as double by default. A long literal in Java is an integer and does not have a decimal point. If you want 1.0 to be treated as a float, you would need to append f to it, like 1.0f. Therefore, the statement that "1.0 is a long literal" is false.
Why other options are wrong
A. Java has two floating-point data types.
This is true. Java has two floating-point data types: float and double. float has a 32-bit precision, while double has a 64-bit precision. Both are used for storing decimal numbers.
B. The following declaration and assignment generates an error: float w = 1.2;
This is true. In Java, the literal 1.2 is treated as a double by default, and you cannot assign a double value directly to a float variable without a cast. The correct way would be float w = 1.2f;.
D. Java has four floating-point data types.
This is false. Java has only two floating-point data types: float and double. There are no other floating-point types in Java.
E. 3.14 is a floating-point number.
This is true. 3.14 is indeed a floating-point number. By default, Java treats numbers with a decimal point as double, unless specified as float by appending an f (e.g., 3.14f).
Which of the following best sums up how relational operators are used in Java?
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They are used to perform arithmetic calculations on two values.
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They are used to compare two values and return a boolean result.
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They are used to assign values to variables.
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They are used to define the scope of variables.
Explanation
Correct Answer
B. They are used to compare two values and return a boolean result.
Explanation
In Java, relational operators are used to compare two values or expressions. These operators return a boolean result (true or false). The common relational operators include ==, !=, <, >, <=, and >=. For example, x > y will return true if x is greater than y and false otherwise.
Why other options are wrong
A. They are used to perform arithmetic calculations on two values.
This is incorrect because arithmetic operations like addition, subtraction, multiplication, and division are done using arithmetic operators such as +, -, *, /, etc., not relational operators.
C. They are used to assign values to variables.
This is incorrect. Assignment of values to variables is done using the assignment operator =, not relational operators.
D. They are used to define the scope of variables.
This is incorrect. The scope of variables is defined by their position in the code and is determined by where they are declared, not by relational operators.
What is the primary advantage of using two's complement representation for signed integers in Java?
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It simplifies the implementation of arithmetic operations
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It allows for larger integer values
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It requires more memory space
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It eliminates the need for a sign bit
Explanation
Correct Answer
A. It simplifies the implementation of arithmetic operations
Explanation
Two's complement representation is widely used for signed integers because it allows for easy and efficient arithmetic operations, including addition and subtraction, without the need for special handling of negative numbers. In two's complement, negative numbers are represented in a way that arithmetic operations can be performed directly using the same hardware without additional logic to check for signs.
Why other options are wrong
B. It allows for larger integer values
This is incorrect because two's complement does not allow for larger integer values than other representations like sign-magnitude. In fact, it may represent one fewer positive value due to how negative numbers are represented.
C. It requires more memory space
This is incorrect because two's complement representation does not require more memory space than other methods of representing signed integers. The size of the number remains the same, but the way negative numbers are encoded is different.
D. It eliminates the need for a sign bit
This is incorrect because two's complement still uses a "sign bit" in the most significant position (the leftmost bit) to indicate whether the number is positive or negative. However, the representation of negative numbers is done in a way that does not require separate handling of the sign bit during arithmetic operations.
From the statements below, pick one that is false.
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The scope of a local variable is the portion of a method over which the variable is known and can be referenced.
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Another name for a class method is a static method.
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A variable of type char can be passed to a method that expects an int argument.
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Primitive types used as method arguments are passed by reference.
Explanation
Correct Answer
D. Primitive types used as method arguments are passed by reference.
Explanation
In Java, primitive types (e.g., int, char, float) are passed by value, not by reference. This means that when a primitive type is passed as an argument to a method, the method gets a copy of the value, not the original variable. Changes made to the parameter inside the method do not affect the original variable.
Why other options are wrong
A. The scope of a local variable is the portion of a method over which the variable is known and can be referenced.
This is correct. The scope of a local variable is limited to the block of code (typically a method) in which it is declared. The variable can only be referenced within that block.
B. Another name for a class method is a static method.
This is correct. A method that belongs to the class, rather than an instance of the class, is referred to as a static method. It can be invoked using the class name and does not require an instance of the class.
C. A variable of type char can be passed to a method that expects an int argument.
This is correct. In Java, a char can be implicitly converted to an int, because a char is represented as a 16-bit Unicode value, which fits within an int. Java automatically converts a char to its corresponding integer value when passed to a method that expects an int.
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