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Questions and Answers
What does an if statement do in Java?
It executes a block of code only if a specified condition is true.
What is the purpose of the if-else statement?
To provide an alternative block to execute when the condition is false.
A ___ statement allows executing a statement or group of statements multiple times.
looping
Which of the following is a repetition control structure?
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What is the function of the break statement in a switch-case statement?
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What kind of exceptions are direct subclasses of Throwable, excluding RuntimeException and Error?
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A try block must be followed by at least one catch block or one finally block.
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What is the role of the catch block in exception handling?
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The while loop tests the condition before executing the loop body.
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In Java, an exception must be one of the throwable class or one of its ___
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What is an assertion in Java?
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Study Notes
Java Statements
- A Java statement is one or more lines of code ending with a semicolon (;).
- Statements generally contain expressions that evaluate to a value.
Control Structures
- Control structures in Java alter the order of execution in a program.
- Two main categories exist:
- Decision Control Structures: Execute specific code blocks while skipping others.
- Repetition Control Structures: Execute a section of code multiple times.
Decision Control Structures
-
If Statement: Executes a block of code only if a specific condition is true.
- If the expression is true, the code inside the if block executes.
- If the expression is false, the code block is skipped.
- If-Else Statement: Extends the if statement by providing an alternative block to execute when the condition is false.
- Nested If Statement: An if statement within another if or else statement, allowing for complex conditional logic.
Switch Case Statement
- A multi-way branch statement, offering a simpler alternative to multiple if-else statements when checking for multiple fixed values.
-
breakStatement: Thebreakstatement defines the end of each case within a switch-case statement. -
defaultStatement: Used to define an alternative message to be displayed when none of the cases match the input value.
Looping Statements
- Used for repeated execution of a statement or a block of statements.
- Common format:
forloop,do-whileloop,whileloop.
For Loop
- A repetition control structure that executes a loop a specific number of times.
- Useful when the number of repetitions is known.
Do-While Loop
- Similar to the while loop, but guarantees to execute at least once because it checks the condition after executing the loop body.
While Loop
- Executes a target statement repeatedly as long as a given condition is true.
- Tests the condition before executing the loop body, meaning it may never execute if the condition is initially false.
Exception Handling
- Deals with errors that occur during program execution.
- Allows for handling unexpected events gracefully.
Exception Hierarchy
-
Error: Represents serious issues in the Java runtime system. -
Checked Exception: Direct subclasses ofThrowableclass (excludingRuntimeExceptionandError). Represents normal errors that can occur during program execution. -
Runtime Exception: Represents exceptions that typically occur at runtime.
Creating Exceptions
- Exceptions can be created using the
throwkeyword, followed by an instance of an exception class.
Generating Exceptions
- Code can generate exceptions using the
throwkeyword, allowing for explicit error handling.
try, catch, and finally Blocks
-
tryBlock: Encloses code that might generate an exception. -
catchBlock: Handles the thrown exception. It is placed after thetryblock and must be of the same class or subclass of the exception thrown. -
finallyBlock: Executes regardless of whether an exception occurs. It is always executed iftryblock, or anycatchblock completes.
Syntax Key Aspects
- The
tryblock is mandatory. - Each
tryblock can have one or morecatchblocks, but at most only onefinallyblock. -
catchblocks andfinallyblocks must be associated with atryblock and follow the order:try,catch,finally. - A
tryblock must be followed by at least onecatchblock or onefinallyblock. - Each
catchblock defines an exception handler. The header of thecatchblock takes exactly one argument: the exception it will handle. - The exception type in the
catchblock must be a subclass ofThrowable.
Assertion in Java
- A mechanism to check assumptions in your code.
- Assertions are not considered normal exception handling.
- Used for debugging and testing, not for handling expected program errors.
throw Clause
- Used within a function to explicitly throw an exception when an error condition is detected.
Why Use Assertion?
- To verify assumptions made about the program state.
- To detect potential bugs early in development.
- To enforce preconditions and postconditions of methods.
Where to Use Assertions?
- For preconditions and postconditions of methods.
- For validating data being passed to sensitive operations.
- To verify internal state consistency.
Where Not to Use Assertions?
- For error handling, as assertions can be disabled.
- For security critical situations, as assertions can disable and bypass critical checks.
Assertion vs. Normal Exception Handling
- Assertion: Verify assumptions and programmer error. They are not meant for handling runtime errors.
- Exception Handling: Deals with unexpected runtime errors or external conditions. They are intended to gracefully handle these events.
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Description
Test your knowledge on Java statements and control structures with this quiz. You'll explore decision control structures like if statements and switch cases, as well as their functions and behaviors in Java programming. Perfect for anyone looking to strengthen their understanding of Java basics.
