Java Fundamentals (D286)
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Free Java Fundamentals (D286) Questions
What is the primary reason for using the short data type in Java instead of the int data type?
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It can store larger values than int
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It requires less memory than int
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It is a floating-point type
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It is used for character data
Explanation
Correct Answer
B. It requires less memory than int
Explanation
The short data type in Java requires less memory than int. While int uses 4 bytes (32 bits) of memory, short uses only 2 bytes (16 bits). This makes short a more memory-efficient choice when dealing with smaller numbers in situations where memory is a concern.
Why other options are wrong
A. It can store larger values than int
This is incorrect because int can store a wider range of values than short. Specifically, an int can store values from -2^31 to 2^31-1, whereas a short can only store values from -2^15 to 2^15-1.
C. It is a floating-point type
This is incorrect because neither short nor int are floating-point types. The floating-point types in Java are float and double.
D. It is used for character data
This is incorrect because while a short can represent some character data in the form of Unicode values, it is not specifically used for character data. The char type is used for individual characters in Java.
Which method of the FileWriter class allows to write additional data to an existing file, if the file does not exist, it will be created?
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public FileWriter(String fileName, Charset charset) {...}
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public FileWriter(String fileName) {...}
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public FileWriter(File file, boolean append) {...}
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public FileWriter(File file) {...}
Explanation
Correct Answer
C. public FileWriter(File file, boolean append) {...}
Explanation
The constructor public FileWriter(File file, boolean append) allows you to specify whether to append to the file or overwrite it. If the file does not exist, it will be created. The append parameter is a boolean value that determines whether data will be added to the end of the file (true) or overwrite the existing data (false).
Why other options are wrong
A. public FileWriter(String fileName, Charset charset) {...}
This constructor allows you to specify the file name and charset but does not provide an option to append to an existing file.
B. public FileWriter(String fileName) {...}
This constructor does not specify whether data should be appended to the file. It overwrites the file if it already exists.
D. public FileWriter(File file) {...}
This constructor is similar to the one in option B, and it overwrites the file if it already exists, without an option for appending.
Which of the following statements accurately describes a local variable in Java?
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A local variable can be accessed from any part of the class.
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A local variable is declared within a method, constructor, or block and is only accessible within that scope.
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A local variable retains its value between method calls.
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A local variable is a type of instance variable that belongs to an object.
Explanation
Correct Answer
B. A local variable is declared within a method, constructor, or block and is only accessible within that scope.
Explanation
Local variables in Java are declared inside methods, constructors, or code blocks. Their scope is limited to the method or block in which they are declared, meaning they cannot be accessed outside of that scope.
Why other options are wrong
A. A local variable can be accessed from any part of the class.
This is incorrect because local variables are restricted to the block, method, or constructor in which they are declared and cannot be accessed outside that scope.
C. A local variable retains its value between method calls.
This is incorrect because local variables are created when the method is called and destroyed when the method exits. They do not retain their values between method calls.
D. A local variable is a type of instance variable that belongs to an object.
This is incorrect because instance variables belong to an object and have a different scope and lifetime compared to local variables, which are confined to a method or block.
Which description about a block in Java programming is correct?
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A segment of code enclosed by a pair of braces {}.
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A segment of code enclosed by a pair of brackets [].
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A segment of code enclosed by a pair of parentheses ().
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A segment of code enclosed by a pair of angular brackets <>.
Explanation
Correct Answer
A. A segment of code enclosed by a pair of braces {}.
Explanation
In Java, a block of code refers to a segment of code that is enclosed by a pair of curly braces {}. This is commonly used to define the body of methods, loops, conditionals, and classes.
Why other options are wrong
B. A segment of code enclosed by a pair of brackets [].
This is incorrect. Square brackets [] are used in Java for array declaration and access, not for defining blocks of code.
C. A segment of code enclosed by a pair of parentheses ().
This is incorrect. Parentheses () are used for method parameters, control flow expressions like if and while, and other operations. They do not define a block of code.
D. A segment of code enclosed by a pair of angular brackets <>.
This is incorrect. Angular brackets <> are used in Java for generics, not for enclosing blocks of code.
Which of the following classes is used to read data from a file in Java?
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BufferedReader
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FileWriter
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PrintWriter
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Scanner
Explanation
Correct Answer
A. BufferedReader
Explanation
In Java, the BufferedReader class is used to read data from files. It provides an efficient way to read text from a file by buffering characters to make reading large files faster. It is commonly used with a FileReader to read files line by line using methods like readLine(). Example:
BufferedReader reader = new BufferedReader(new FileReader("file.txt"));
String line = reader.readLine();
Why other options are wrong
B. FileWriter
This is incorrect because FileWriter is used to write data to a file, not to read it. It allows writing character data to a file.
C. PrintWriter
This is incorrect because PrintWriter is used to write formatted text to a file or to the console. It does not read data from a file, making it unsuitable for input operations.
D. Scanner
This is incorrect because while the Scanner class can be used for reading data from various sources (including files), it is not as efficient for reading large files compared to BufferedReader. Scanner is generally used for reading input from the console.
Post-decrement operator is denoted by:
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m++;
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++m;
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--m;
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m--;
Explanation
Correct Answer
D. m--;
Explanation
In Java, the post-decrement operator is written as m--. This operator decreases the value of m by 1, but the original value of m is used in the expression before the decrement takes place. It's distinct from the pre-decrement operator (--m), which decrements the value first before using it in the expression.
Why other options are wrong
A. m++;
This is incorrect because m++ is the post-increment operator. It increases the value of m by 1 after its current value is used in an expression. It performs the opposite action of a post-decrement.
B. ++m;
This is incorrect because it is the pre-increment operator. It increases the value of m by 1 before the value is used in an expression. It does not denote a post-decrement operation.
C. --m;
This is incorrect because it represents the pre-decrement operator. It decreases the value of m by 1 before it is used in an expression. While it does perform a decrement, the timing of the decrement relative to its use in an expression makes it different from the post-decrement operator.
What is the maximum positive value that can be stored in a byte data type in Java?
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127
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255
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128
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-128
Explanation
Correct Answer
A. 127
Explanation
In Java, the byte data type is an 8-bit signed integer, which means it can hold values from -128 to 127. The range is determined by the formula: –2⁷ to 2⁷–1. Therefore, the maximum positive value a byte can store is 127.
Why other options are wrong
B. 255
This is incorrect because 255 is the maximum value of an unsigned 8-bit number. However, in Java, the byte type is signed by default, so its range only goes up to 127. The value 255 would require a larger data type like int or short or an unsigned context, which Java doesn't use for the byte type.
C. 128
This is incorrect because 128 is one value above the maximum positive limit of a signed 8-bit integer. Trying to assign 128 to a byte in Java would result in a compile-time error due to overflow.
D. -128
This is wrong because the question specifically asks for the maximum positive value, and -128 is the minimum value a byte can store, not the maximum. It represents the lower bound, not the upper.
Out of these, which is untrue?
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Java is object-oriented
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Java is an interpreted language
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Java supports inheritance, encapsulation, and polymorphism
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Java is a procedural language
Explanation
Correct Answer
D. Java is a procedural language
Explanation
Java is primarily an object-oriented programming language, meaning it focuses on objects and classes. It supports key object-oriented principles such as inheritance, encapsulation, and polymorphism. Java is not a procedural language, which focuses more on functions and sequences of steps. Java also uses both compilation and interpretation, meaning it compiles into bytecode that is interpreted by the Java Virtual Machine (JVM), but it is primarily considered an object-oriented language.
Why other options are wrong
A. Java is object-oriented
This is true. Java is an object-oriented language, meaning it is built around objects and classes, which encapsulate data and functionality.
B. Java is an interpreted language
This is true. Java code is compiled into bytecode, which is then interpreted by the JVM. This is why Java is considered both a compiled and interpreted language.
C. Java supports inheritance, encapsulation, and polymorphism
This is true. Java supports all three main principles of object-oriented programming: inheritance (where a class can inherit fields and methods from another class), encapsulation (wrapping data and methods into a single unit), and polymorphism (the ability to take on different forms, such as method overloading and overriding).
What are literals?
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Used to combine expressions
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Stores and identify the value
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A representation of a specific value
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Used for translating languages
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Writing an algorithm
Explanation
Correct Answer
C. A representation of a specific value
Explanation
In programming, literals are fixed values that are directly represented in the code. They stand for a specific value, such as numbers, characters, strings, or booleans, and are used to represent constant values. For example, 42, "Hello", true, and 'a' are all literals in Java. They are not computed or changed during the execution of the program, and their purpose is to represent exact values used in expressions or assignments.
Why other options are wrong
A. Used to combine expressions
This is incorrect because literals are not used to combine expressions. They represent specific values directly, while expressions combine variables, constants, and operators to perform operations.
B. Stores and identify the value
While literals represent specific values, they do not "store" the value. The literal itself is the direct representation, and variables are used to store values in memory.
D. Used for translating languages
This is incorrect because literals have nothing to do with translating languages. They are just fixed values used in programming, not related to language translation.
E. Writing an algorithm
This is incorrect because literals are not algorithms. They are specific values used in programs, while algorithms describe the steps to solve a problem.
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.
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