Interview Questions and Answers for 'Java' | Search Interview Question

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Q1321. Is String thread-safe?

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Q1322. Explain toString method ? Which class contains this method ?

Core Java

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Q1323. Explain pre compilation.

Core Java

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Q1324. What will the following code print and Why

class Class1 {
static{
System.out.println("Wow");
}
public static final int xyz=1;
}

class Class2{
public static void main(String[] args) {
System.out.println(String.valueOf(Class1.xyz));
}
}

Core Java

Ans. 1

Reason being that Class1.xyz is replaced with 1 during pre compilation only and a reference to Class1 is never made.

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Q1325. Why java allows explicit import of class final static elements but not others ?

Core Java

Ans. Because they can be replaced easily in pre compilation whereas others cannot.

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Q1326. Why do we have multiple core java jars in java 9 ?

Core Java

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Q1327. What is the concept of modules in Java 9 ?

Core Java

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Q1328. How modules are different than packages in Java 9 ?

Core Java

Ans. Modules are independently build units and contains multiple packages.

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Q1329. How Java 9 helps in building light weight applications ?

Core Java

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Q1330. Do we need different class loaders for different modules in Java 9 ?

Core Java

Ans. No, We can use the same class loader.

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Q1331. What is ModuleDescriptor ?

Core Java

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Q1332. What is ModuleLayer ?

Core Java

Ans. A Module layer is created from a graph of modules and is a function that maps modules to their class loaders.

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Q1333. Difference between named and unnamed modules ?

Core Java

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Q1334. What is the use of Requires, Exports, Opens and provides within Module Descriptor ?

Core Java

Ans. Requires specifies the dependencies for the module, i.e the modules required for this module to function.

Exports specifies the packages exported by the module.

Opens specifies the packages opened by the module.

Provides specifies the services provided by the module

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Q1335. Does Java 9 allows same package within different modules ?

Core Java

Ans. Yes it allows if the modules are mapped to different class loaders.

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Q1336. What are the qualified and unqualified packages ?

Core Java

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Q1337. How does modularity in Java 9 facilitates better encapsulation ?

Core Java

Ans. By providing dependencies , services and exports explicitly

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Q1338. How does Java 9 provides backward compatibility with libraries that haven't published themselves as modules ?

Core Java

Ans. Though Automatic modules. Any JAR on the module path without module descriptor ends up as automatic module

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Q1339. What is the default setting for Automatic modules regarding exporting packages and reading modules ?

Core Java

Ans. As one purpose of automatic module is to provide backward compatibility with the module less dependencies, automatic modules exports all packages and include all other modules.

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Q1340. What is JShell?

Core Java

Ans. JShell is a feature in java 9 using which we can code and test without compiling using javac and see the result of calculations directly.

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Q1341. Can we have private methods in interfaces ?

Core Java

Ans. Yes, With Java 9

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Q1342. What could be the reason for allowing private methods in java 9 ?

Core Java

Ans. Java 8 allowed for method implementation using default methods in interfaces. As those default methods could contain complex logic and might need organizing the logic into multiple methods, they have allowed for private methods.

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Q1343. What is the difference between implementing interfaces and inheritance in Java ?

Core Java

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Q1344. What is a weak reference ?

Core Java

Ans. A weak reference is a reference that gets removed on the next garbage collection cycle.

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Q1345. Write a program that count the number of access to a method?

Core Java

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Q1346. Can you explain following exception

java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result.

Core Java

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Q1347. What are we doing here

list.stream().collect(Collectors.groupingBy(ClassA::getElement1,
Collectors.averagingDouble(ClassA::getelement2)));

Core Java

Ans. We are averaging elements of a collection by element1 grouped by element1

* list is the reference of collection
* element1 is the member element returned by getElement1 method of ClassA
* element2 is the member element returned by getElement2 method of ClassA

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Q1348. What will the following code return

list.stream().collect(Collectors.groupingBy(ClassA::getElement1,
Collectors.averagingDouble(ClassA::getElement2)));

Core Java

Ans. Map<DataType1,DataType2> where DataType1 is the data type of element1 ( returned by getelement1 method ) and DataType2 is the data type of element2 ( returned by getElement2 method )

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Q1349. What is the advantage of BidDecimal over Double ?

Core Java

Ans. BigDecimal provides more precision as compared to double.

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Q1350. What is the difference between following rounding modes

RoundingMode.CEILING
RoundingMode.DOWN
RoundingMode.FLOOR
RoundingMode.HALF_DOWN
RoundingMode.HALF_UP
RoundingMode.HALF_EVEN

Which is the one you use often and Why ?

Core Java

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