Which of these is the correct way to write a Runnable as a lambda?
Answer: C
Correct answer: Runnable r = () -> System.out.println("go");
A lambda for Runnable takes no parameters and returns nothing, so it is an empty parameter list, the arrow token, and a statement. The arrow is -> and not =>; no return type is written; and adding a parameter would not match run(), which takes none.
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Which of these exception types is checked?
Answer: D
InterruptedException extends Exception, so it must be caught or declared, which is why every call to sleep or join needs a try block. The other three extend RuntimeException and are unchecked, so the compiler says nothing about them.
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Which of these classes does Thread extend?
Answer: A
Thread extends Object like any class with no other superclass, and separately implements the Runnable interface. ThreadGroup is a container Thread refers to rather than a parent class, and Process is unrelated, describing an operating system process.
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Which of these correctly names a thread at construction time?
Answer: B
The two-argument constructor takes the Runnable first and the name second. There is no builder-style name method, and single quotes make a char literal rather than a String. setName can also be used after construction.
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Which of these is NOT a method declared on Thread?
Answer: C
notifyAll is declared on Object, so Thread has it only by inheritance, as every class does. setName, getState and isDaemon are all genuine Thread members. The distinction matters when reading which class the documentation puts a method under.
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Which of these is a legal way to synchronize on a private lock object?
Answer: D
The statement takes a parenthesised expression followed by a BLOCK in braces, so both the parentheses and the braces are required. Unlike if or for, a synchronized statement cannot take a single statement without braces, and there is no method form.
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Which of these declarations does the compiler reject?
Answer: A
synchronized describes how a method body acquires a lock, and an abstract method has no body, so the two cannot be combined. An abstract declaration on its own is fine, as is synchronized on any method that does have a body.
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What is the return type of Thread.interrupted()?
Answer: B
Correct answer: boolean
Thread.interrupted() reports whether the current thread has been interrupted and clears the flag as it does so, which is the trap in the name. isInterrupted() is the instance method that reports without clearing, and confusing the two loses interrupts.
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Which of these correctly starts a thread?
Answer: C
Correct answer: t.start();
start() creates the new thread of execution and arranges for run() to be called on it. Calling run() directly compiles and executes the code, but on the calling thread - so nothing runs concurrently, which is the classic beginner’s error.
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Which of these is the correct signature of ExecutorService.submit for a Callable?
Answer: D
Correct answer: <T> Future<T> submit(Callable<T> task)
Submission is asynchronous, so the method returns immediately with a Future standing for the eventual result rather than the result itself. The type parameter ties the future’s type to the callable’s, so get() returns the right type without a cast.
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