Java Programming

Java OOP, collections, multithreading

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Difficulty: All Easy Medium Hard 111–120 of 476

Topics in Java Programming

All Basics & Syntax 100 OOP in Java 100 Collections Framework 100 Multithreading 100 Exception Handling 100 I/O Streams 100 JDBC 100 Generics 100 Lambda Expressions 100 Spring Framework Basics 58

Q.111 Medium Generics

Which statement correctly defines a generic class with multiple type parameters and bounds?

A class Container { }

B class Container extends Number { }

C class Container { }

D class Container extends { }

Correct Answer: C. class Container { }

EXPLANATION

Multiple type parameters with bounds must be comma-separated and each can have its own upper bound. Option C shows correct syntax with recursive bound on T and bound on K.

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Q.112 Medium Generics

Consider the declaration: List

A List of Integer and its subclasses

B List of Integer and its superclasses

C List of any type

D List of Number and Integer only

Correct Answer: B. List of Integer and its superclasses

EXPLANATION

'? super Integer' is a lower bounded wildcard that accepts Integer and all its superclasses like Number, Object. This allows write operations with Integer values.

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Q.113 Medium Generics

Which statement about generic type parameters is TRUE?

A Type parameters must be uppercase single letters (T, U, V, etc.)

B Type parameters can only be used in class declarations, not in method declarations

C Type parameters can be any valid Java identifier

D Type parameters must match the actual type used at instantiation

Correct Answer: C. Type parameters can be any valid Java identifier

EXPLANATION

While convention uses single uppercase letters, type parameters can be any valid identifier. Statements B and D are also incorrect.

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Q.114 Medium Generics

What is the significance of the '&' operator in generic bounds like ''?

A T must extend both A and B (multiple bounds)

B T must extend A or B

C It's a bitwise AND operation

D T extends A with B as an alternative

Correct Answer: A. T must extend both A and B (multiple bounds)

EXPLANATION

Multiple bounds (using &) mean T must satisfy all constraints. This is useful when a type needs to implement multiple interfaces.

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Q.115 Medium Generics

Consider the method: public static T getFirst(List list) { return list.get(0); }

How would you call this method for a List?

A String result = Main.getFirst(stringList);

B String result = getFirst(stringList);

C String result = Main.getFirst(stringList);

D Both A and B are correct

Correct Answer: D. Both A and B are correct

EXPLANATION

Type inference in Java allows the compiler to deduce T from the argument type, so both explicit and implicit type specification work.

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Q.116 Medium Generics

What is the relationship between raw types and generics in Java?

A Raw types are legacy code that bypasses generic type checking

B Raw types are automatically converted to generic types

C Raw types and generics cannot coexist

D Raw types are more efficient than generics

Correct Answer: A. Raw types are legacy code that bypasses generic type checking

EXPLANATION

Raw types (like 'List' without type parameters) are legacy and should be avoided as they bypass compile-time type safety.

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Q.117 Medium Generics

Which generic wildcard usage is INCORRECT?

A List

B List

C Map map;

D List

Correct Answer: D. List

EXPLANATION

Nested wildcards like '? extends ? super T' are not allowed. Wildcards cannot be combined or nested.

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Q.118 Medium Generics

In a generic class 'class Box', what constraint is placed on T?

A T must implement the Comparable interface with itself as the type parameter

B T must be a subclass of Comparable

C T must be Comparable with any type

D T is unrestricted and Comparable is optional

Correct Answer: A. T must implement the Comparable interface with itself as the type parameter

EXPLANATION

The bound 'T extends Comparable<T>' ensures T is comparable to itself, enabling type-safe comparison operations.

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Q.119 Medium Generics

What does the PECS principle stand for in generics context?

A Producer Extends, Consumer Super

B Parameter Extends, Class Super

C Polymorphic Extends, Constructor Super

D Public Extends, Static Super

Correct Answer: A. Producer Extends, Consumer Super

EXPLANATION

PECS guides when to use upper bounds (? extends) for producers/readers and lower bounds (? super) for consumers/writers.

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Q.120 Medium Generics

Which generic declaration would allow storing both String and Integer in the same collection?

A List list = new ArrayList();

B List list = new ArrayList();

C List

D All of the above

Correct Answer: D. All of the above

EXPLANATION

All three allow storing multiple types because they use unbounded or Object-level wildcards, though List<?> is most restrictive for additions.

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