11. How to time operations in Java
There are two standard ways to time operations in
Java: System.currentTimeMillis() and System.nanoTime() The question is, which
of these to choose and under what circumstances. In principle, they both
perform the same action but are different in the following ways:
1. System.currentTimeMillis takes somewhere between
1/1000th of a second to 15/1000th of a second (depending on the system) but
System.nanoTime() takes around 1/1000,000th of a second (1,000 nanos)
2. System.currentTimeMillis takes a few clock
cycles to perform Read Operation. On the other hand, System.nanoTime() takes
100+ clock cycles.
3. System.currentTimeMillis reflects Absolute Time
(Number of millis since 1 Jan 1970 00:00 (Epoch Time)) but System.nanoTime()
does not necessarily represent any reference point.
12. Choice between Float and Double
Data type Bytes
used Significant figures (decimal)
Float 4 7
Double 8 15
Double is often preferred over float in software
where precision is important because of the following reasons:
Most processors take nearly the same amount of
processing time to perform operations on Float and Double. Double offers far
more precision in the same amount of computation time.
13. Computation of power
To compute power (^), java performs Exclusive OR
(XOR). In order to compute power, Java offers two options:
1. Multiplication:
1 double
square = double a * double a; // Optimized
2 double
cube = double a * double a * double a;
// Non-optimized
3 double
cube = double a * double square; // Optimized
4 double
quad = double a * double a * double a * double a; // Non-optimized
5 double
quad = double square * double square; // Optimized
4. pow(double
base, double exponent):‘pow’ method is used to calculate where multiplication
is not possible (base^exponent)
1 double
cube = Math.pow(base, exponent);
Math. pow should be used ONLY when necessary. For
example, exponent is a fractional value. That is because Math.pow() method is
typically around 300-600 times slower than a multiplication.
14. How to handle Null Pointer Exceptions
Null Pointer Exceptions are quite common in Java.
This exception occurs when we try to call a method on a Null Object Reference.
For example,
1 int
noOfStudents = school.listStudents().count;
If in the above example, if get a
NullPointerException, then either school is null or listStudents() is Null.
It’s a good idea to check Nulls early so that they can be eliminated.
1 private
int getListOfStudents(File[] files) {
2 if (files == null)
3 throw new
NullPointerException("File list cannot be null");
4 }
15. Encode in JSON
JSON (JavaScript Object Notation) is syntax for
storing and exchanging data. JSON is an easier-to-use alternative to XML. Json
is becoming very popular over internet these days because of its properties and
light weight. A normal data structure can be encoded into JSON and shared
across web pages easily. Before beginning to write code, a JSON parser has to
be installed. In below examples, we have used json.simple
(https://code.google.com/p/json-simple/).
Below is a basic example of Encoding into JSON:
01 import
org.json.simple.JSONObject;
02 import
org.json.simple.JSONArray;
03
04 public class
JsonEncodeDemo {
05
06 public static void main(String[] args) {
07
08 JSONObject obj = new JSONObject();
09 obj.put("Novel Name",
"Godaan");
10 obj.put("Author",
"Munshi Premchand");
11
12 JSONArray novelDetails = new
JSONArray();
13 novelDetails.add("Language:
Hindi");
14 novelDetails.add("Year of
Publication: 1936");
15 novelDetails.add("Publisher:
Lokmanya Press");
16
17 obj.put("Novel Details",
novelDetails);
18
19 System.out.print(obj);
20 }
21 }
Output:
1 {"Novel
Name":"Godaan","Novel Details":["Language:
Hindi","Year of Publication: 1936","Publisher: Lokmanya
Press"],"Author":"Munshi Premchand"}
