Core java interview Questions You'll Most Likely Be Asked (Second Edition)

Suppose you are reading 10000 String values from the
database. You need to create a concatenated String with
these values. Which is the most efficient way to achieve
this?
Answer:
There are several ways in which you can concatenate String
values. The mostly commonly used method is to use the
concatenation operator (+). However, this is not at all efficient in
terms of performance and should be avoided when you have a
large number of Strings. This is because the String class is
immutable. So, using the + operator results in the creation of a
large number of Strings. Java provides the StringBuffer class.
This has a method called append that can be used to create
concatenated Strings. This has better performance since it is a
mutable class. There is also another class called StringBuilder
which is very similar to StringBuffer. The only difference is that
StringBuffer is synchronized while StringBuilder is not. So
StringBuilder has a slightly better performance compared to

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287.
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StringBuffer. So, if synchronization is not an issue, you can use
StringBuilder, otherwise you can use StringBuffer.
Suppose you are developing an application that performs
a lot of mathematical calculations involving very large
decimal numbers. Which data type will you use for your
variables given that precision is important?
Answer:
Normally, programmers use float or double data types while
dealing with decimal numbers. However, these data types have a
downside. While dealing with very large or very small numbers, a
loss of precision can occur with these data types leading to
inaccurate results. So, using these data types in situations where
precision is important is not a good idea. Java provides a class
called java.lang.BigDecimal. This class overcomes the
limitations of the float and double data types. It does not lose
precision while dealing with large or small numbers and therefore
provides exact results. It has methods corresponding to all the
arithmetic operations like addition, subtraction, multiplication and
division. In addition, it supports a lot of other operations as well.
So, it can be used to perform all mathematical operations and
provides precise results. The only downside of BigDecimal is
performance. However, if precision is a priority over performance,
then BigDecimal should be used.