Tag: java
Questions Related to java
Which collection class allows you to grow or shrink its size and provides indexed access to its elements, but whose methods are not synchronized?
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java.util.HashSet
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java.util.LinkedHashSet
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java.util.List
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java.util.ArrayList
AI Explanation
To answer this question, you need to understand the characteristics of different collection classes in Java.
Option A) java.util.HashSet - This option is incorrect because HashSet does not provide indexed access to its elements. It does not maintain the order of its elements either.
Option B) java.util.LinkedHashSet - This option is incorrect because LinkedHashSet does not provide indexed access to its elements. It maintains the insertion order of its elements.
Option C) java.util.List - This option is incorrect because List is an interface, not a specific implementation. It can be implemented by various classes such as ArrayList, LinkedList, etc.
Option D) java.util.ArrayList - This option is correct because ArrayList allows you to grow or shrink its size dynamically. It provides indexed access to its elements, meaning you can access elements using their positions in the list. However, the methods of ArrayList are not synchronized, which means they are not thread-safe.
The correct answer is Option D. ArrayList is the collection class that allows you to grow or shrink its size, provides indexed access to its elements, and its methods are not synchronized.
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java.util.Map
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java.util.Set
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java.util.List
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java.util.Collection
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Java.util.Map
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Java.util.List
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Java.util.HashTable
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Java.util.Collection
Hash table based implementation of the Map interface.
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Java.util.Map
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Java.util.Set
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Java.util.List
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Java.util.Collection
An object that maps keys to values. A map cannot contain duplicate keys; each key can map to at most one value.
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java.util.ArrayList
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java.util.LinkedHashMap
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java.util.HashMap
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java.util.TreeMap
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java.util.SortedMap
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java.util.TreeMap
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java.util.TreeSet
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java.util.Hashtable
To solve this question, the user needs to have a basic understanding of Java collections and their functionalities. Specifically, they need to be familiar with the concept of accessing elements by associating a key with a value and the concept of synchronization in Java collections.
Now, let's go through each option and explain why it is right or wrong:
A. java.util.SortedMap: This option is incorrect. While a SortedMap allows you to access its elements by associating a key with an element's value, it does not provide synchronization. To ensure thread-safe access to a SortedMap, you would need to use additional synchronization mechanisms such as the Collections.synchronizedSortedMap() method.
B. java.util.TreeMap: This option is incorrect. Although a TreeMap allows you to access its elements by associating a key with an element's value, it does not inherently provide synchronization. To achieve synchronized access to a TreeMap, you would need to use additional synchronization mechanisms such as the Collections.synchronizedSortedMap() method.
C. java.util.TreeSet: This option is incorrect. A TreeSet is not a collection class that allows you to access elements by associating a key with an element's value. It is an implementation of the Set interface that stores elements in a sorted and unique order.
D. java.util.Hashtable: This option is correct. Hashtable is a collection class in Java that allows you to access its elements by associating a key with an element's value. It also provides synchronization, meaning that multiple threads can safely access and modify the Hashtable concurrently without causing data inconsistency or other concurrency issues.
Therefore, the correct answer is:
The Answer is: D. java.util.Hashtable
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float f = 1F;
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float f = 1.0;
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float f = "1";
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float f = 1.0d;
What is the numerical range of char?
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0 to 32767
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0 to 65535
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-256 to 255
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-32768 to 32767
AI Explanation
To answer this question, we need to understand the numerical range of the char data type.
In Java, the char data type represents a single character and is stored as a 16-bit unsigned integer. The numerical range of char is from 0 to 65535.
Let's go through each option to understand why it is correct or incorrect:
Option A) 0 to 32767 - This option is incorrect because it does not cover the full range of char values.
Option B) 0 to 65535 - This option is correct because it represents the full numerical range of the char data type.
Option C) -256 to 255 - This option is incorrect because it does not cover the positive range of char values.
Option D) -32768 to 32767 - This option is incorrect because it includes negative values, while char is an unsigned data type.
The correct answer is Option B. This option is correct because it represents the full numerical range of the char data type, which is from 0 to 65535.
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It can extend exactly one class and implement exactly one interface.
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It can extend exactly one class and can implement multiple interfaces.
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It can extend exactly one class or implement exactly one interface.
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It can implement multiple interfaces regardless of whether it also extends a class.
To answer this question, one needs to understand the concept of an anonymous inner class in Java.
An anonymous inner class is a class that is defined and instantiated at the same time, without explicitly giving it a name. It is typically used when you need to create a class that is used only once and does not need to be reused.
Now let's go through each option and explain why it is right or wrong:
A. It can extend exactly one class and implement exactly one interface. This option is incorrect. An anonymous inner class can extend a class or implement an interface, but it cannot do both at the same time. It can either extend a class or implement an interface, but not both simultaneously.
B. It can extend exactly one class and can implement multiple interfaces. This option is incorrect. As mentioned earlier, an anonymous inner class cannot extend a class and implement multiple interfaces at the same time. It can either extend a class or implement an interface, but not both simultaneously.
C. It can extend exactly one class or implement exactly one interface. This option is correct. An anonymous inner class can either extend a class or implement an interface. It cannot do both at the same time, but it can choose to extend a class or implement an interface based on the requirements.
D. It can implement multiple interfaces regardless of whether it also extends a class. This option is incorrect. An anonymous inner class can implement multiple interfaces, but only if it does not extend a class. If it extends a class, it can only implement one interface.
Therefore, the correct answer is:
The Answer is: C
Which is true about a method-local inner class?
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It must be marked final.
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It can be marked abstract.
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It can be marked public.
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It can be marked static.
AI Explanation
To answer this question, let's go through each option to understand why it is correct or incorrect:
Option A) It must be marked final - This option is incorrect. Method-local inner classes do not have any restrictions on being marked as final. They can be marked as final, but it is not a requirement.
Option B) It can be marked abstract - This option is correct. Method-local inner classes can be marked as abstract. This allows the class to have abstract methods that must be implemented by any non-abstract subclasses.
Option C) It can be marked public - This option is incorrect. Method-local inner classes cannot be marked as public. They can only have either default (package-private) or private access modifiers.
Option D) It can be marked static - This option is incorrect. Method-local inner classes cannot be marked as static. They are implicitly associated with an instance of the enclosing class and cannot exist without an instance of the enclosing class.
Therefore, the correct answer is B) It can be marked abstract. This option is correct because method-local inner classes can be marked as abstract and have abstract methods.
Please select the most appropriate option.