Computer scienceProgramming languagesKotlinConcurrency and parallelismParallelismSynchronization

Monitor and Thread synchronization

Initialize fields only once

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Here's a class named SimpleClass. It has a single field of the String type and a method to initialize the field. The method writes a given value to the field if it's empty. Otherwise, the method does nothing.

class SimpleClass {

    var str: String = ""

    fun initWithString(str: String) {
        if (this.str.isEmpty()) { // 1
            this.str = str        // 2
        }                         // 3
    }
}

Multiple threads are trying to invoke the method initWithString on the same instance. How can you synchronize this code so that the field of the instance gets initialized only once? Select all correct cases:

Select one or more options from the list

Nothing needs to be done, everything works correctly

Declare the class with the @Synchronized annotation

Declare the method with the @Synchronized annotation

Put line 2 in a synchronized block, the monitor should be the instance (this)

Declare the field str with the synchronized keyword

Put lines 1–3 in a synchronized block, the monitor should be the instance (this)

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