Questions and Answers
The command ___ executes a Java application.
java
The .class extension on a file means that the file:
is produced by the Java compiler
Which of the following statements about Java Class Libraries is false? (Select all that apply)
Which of the following statements is true? (Select all that apply)
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Which of the following statements is true? (Select all that apply)
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Which command executes the Java class file Welcome.class?
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What is the output of the following statements? System.out.print( 'Hello '); System.out.println( 'World' );
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The format specifier ________ is a placeholder for an int value.
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Given the Java statement number1 = input.nextInt(); what occurs if the user does not enter a valid int value?
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What must the filename be for the public class that begins with 'public class Addition'?
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Each class you create becomes a new ________ that can be used to declare variables and create objects.
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You must call most methods other than ________ explicitly to tell them to perform their tasks.
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Declaring instance variables ________ is known as data hiding or information hiding.
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Reference-type variables (called references) store ________ in memory.
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Java requires a ________ call for every object that's created.
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The control variable of a counter-controlled loop should be declared as ________ to prevent errors.
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Study Notes
Java Basics
- The command
javais used to execute a Java application. - Files with the
.classextension are generated by the Java compiler, indicating they contain compiled Java bytecode.
Java Class Libraries
- Java class libraries, also known as Java APIs, are not portable; this statement is false.
- They provide pre-designed, tested classes that reduce development effort.
Methods in Java
- A method is essential for performing tasks in a program, containing statements that execute specific functions.
- Methods abstract their inner workings from users, similar to how a car's accelerator hides its mechanisms.
Compiled vs. Interpreted Programs
- Compilers convert high-level programs into machine language, whereas interpreted programs do not necessarily run faster than compiled programs.
Executing Java Classes
- The command
java Welcomeexecutes the Java class fileWelcome.class. - Output example:
System.out.print("Hello "); System.out.println("World");prints "Hello World".
Format Specifiers
- The format specifier
%dis a placeholder for integer values in Java.
Error Handling
- Entering an invalid integer value using
input.nextInt()whilenumber1is defined as an int results in a runtime logic error.
Class File Naming
- The public class name must match the filename; for a class
public class Addition, the filename should beAddition.java.
Object and Variable Management
- Each created class introduces a new type that can be used for variable declaration and object creation.
- Most methods, except for
main, require explicit calls to operate.
Data Encapsulation
- Declaring instance variables as
privateimplements data hiding, protecting the variable's state from outside access.
Memory Management
- Reference-type variables in Java store the memory address of an object rather than the actual object itself.
- A constructor call is mandatory for creating every object in Java.
Control Structures
- Control variables in counter-controlled loops should be declared as
intto prevent errors and ensure proper iteration management.
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Test your knowledge of Java programming concepts with these flashcards. Each card presents a key term or concept related to Java, along with its definition or explanation. Ideal for beginners looking to understand the basics of Java.
