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

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Q1301. Is HttpServlet an abstract class ?

Java EE

Ans. Yes

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Q1302. Why do we need ConcurrentHashMap ?

Core Java

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Q1303. What is the default size of ArrayList ?

Core Java

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Q1304. Find minimum operations required to convert one string to another. Allowed operation :Insertion Deletion Replace, all operational costs are same.

Core Java

Ans. StringBuilder str = new StringBuilder("Pizza");
int size = str.length();
str = str.replace(size-1, size, "u");
System.out.println("After replace, str = " str); // prints Pizzu

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Q1305. Write code to read data from a file and write it to a file with 2 threads using the thread name content

Core Java

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Q1306. What is the need for filters in Java Servlets ?

Java EE

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Q1307. What is the difference between Interfaces and Abstract Classes with respect to Java 8 ?

Core Java

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Q1308. Which of the OOP's feature - encapsulation or abstraction - is more important ?

Core Java

Ans. Encapsulation facilitates security by hiding data and logic whereas Abstraction simplifies organization of data and related logic.

As applications scale, both concepts are required for easy management and maintenance. Encapsulation for security and criss cross communication between objects / modules will make it vulnerable. and Abstraction for better organization that enables better understanding of application code and easy maintainability.

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Q1309. Which of the polymorphism type - static or runtime - is more important ?

Core Java

Ans. Method overloading / static polymorphism compared to method overriding / runtime polymorphism has very limited usage as it just opens up an alternate way of defining a different method with the same name.

Method Overriding on other hand opens up many other features like contracting , interfacing , pluging development and hence development of libraries and frameworks.

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Q1310. What is the reason that non-static method are not allowed to be referenced from a static context in Java?

Core Java

Ans. If we try to access an instance method from a static context , the compiler has no way to guess which instance method ( variable for which object ), you are referring to. Though, you can always access it using an object reference.

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Q1311. Which are the thread safe / synchronized / concurrent classes in java collections ?

Core Java

Ans. Stack
Properties
Vector
BlockingQueue
ConcurrentMap
ConcurrentNavigableMap

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Q1312. What are the differences between Intermediate and Terminal Operations in Java 8 streams?

Core Java

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Q1313. What is the difference between Collections.emptyList() and creating instance of a list ?

Core Java

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Q1314. Which are the classes that implement java.util.List interface ?

Core Java

Ans. ArrayList
LinkedList
Vector
Stack

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Q1315. Why do you think that Stack collection class implement List interface ?

Core Java

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Q1316. What is the there only one method declared in Runnable interface?

Core Java

Ans. The Runnable interface describes a class whose instances can be run as a thread. The interface itself is very simple, describing only one method ( run ) that is called automatically by Java when the thread is started. The Runnable interface is usually used in conjunction with the Thread class.

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Q1317. What is difference between Executor.submit() and Executer.execute() method ?

Core Java

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Q1318. What is difference between CyclicBarrier and CountDownLatch in Java ?

Core Java

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Q1319. What do you mean by synchronized Non Access Modifier?

Core Java

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Q1320. Name few classes of java.util.regex package ?

Core Java

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Q1321. Is String thread-safe?

Core Java

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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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