Java Barcode API

While declaring the class member variables we have to be very confident about the behavior of the member variables. For example some variable are constant and will be same across the class life cycle and some are instance variables which will be tightly bind with the object (instance) of the class.

When an instance of a class is created using new, initialization of the class’s instance variables create for each unique instance.

Always use the static for the member variable which doesn’t change across the objects of the class.

I would try to check the performance using the below code sample:

public class TestClassVariable {

public TestClassVariable() {

// do nothing

}

public String country[] = { “India”, “USA”, “China”, “UK” };

public static void main(String s[]) {

long start, end;

int[] a = new int[1000000];

start = System.currentTimeMillis();

for (int j = 0; j length; j++) {

TestClassVariable tstClassVar = new TestClassVariable();

}

end = System.currentTimeMillis();

System.out.println(end – start + ” “

+ ” milli seconds execution time”);

}

}

Result: 94 milli seconds execution time

In the above code we used country as class instance variable and it takes 94MS but as we know country could be make as static member variable because it will be not going to change across the instances so the correct way to use as static member variable.

So we can change the program slightly and see the figures again

public class TestClassVariable {

public TestClassVariable() {

// do nothing

}

public static String country[] = { “India”, “USA”, “China”, “UK” };

public static void main(String s[]) {

long start, end;

int[] a = new int[1000000];

start = System.currentTimeMillis();

for (int j = 0; j length; j++) {

TestClassVariable tstClassVar = new TestClassVariable();

}

end = System.currentTimeMillis();

System.out.println(end – start + ” “

+ “milli seconds execution time”);

}

}

Result: 16 milli seconds execution time

We could easily figure it out the performance get enhance 6 times then the original one

We could use to create the object inside or outside of the loop depends upon the behavior of the class.
If any class having class member variable then class needs to be inside the loop and that will limit their scope which is good to garbage collect but if class used as Utility class and doesn’t have member class variable then we could declare the class out side of the loop and used inside the loop.
Below example shows there are only 32 ms would take to instantiate the object inside the loop but best thing is that it would limit the scope which is good during garbage collection

public class TestLoop {
public static void main(String s[]) {
long start, end;
int[] a = new int[1000000];
start = System.currentTimeMillis();
TestName tname1 = new TestName();
for (int i = 0; i
// tname1=new TestName();
}
end = System.currentTimeMillis();
System.out.println(end – start + ” milli “
+ “seconds for One Time Loop”);
start = System.currentTimeMillis();
for (int j = 0; j
TestName tname = new TestName();
}
end = System.currentTimeMillis();
System.out.println(end – start + ” “
+ “milli seconds loop calling object inside Loop “);
}
}
Result: 0 milli seconds for One Time Loop
32 milli seconds for loop calling object inside Loop

As per above example you could see the declaring the object inside loop doesn’t have much impact on performance.

In below example explain the two ways to declare the object option 1 inside declaration and option 2 out side declaration.

Option 1:
for (int i=0; i
{
Object obj = tempList.get(i);
o. doOperation();
}
Option 2:
Object o;
for (int i=0; i
{
o = tempList.get(i);
o.doOperation();
}

We could say that Option1 better as it restricts scope of ‘obj’ variable to the for block. From a performance perspective, it might not have any effects in Java, but it might have in lower level compilers. They might put the variable in a register if you do the first.
Construction of an object using new is totally different from just declaring it, of course.
I think readability is more important than performance and from a readability standpoint, the first code is definitely better.
But if you have utility class which doesn’t have member variables we could instantiate once and reuse across the code.

In the below example I am trying to explain the utility class which could be instantiate once and use across the application.

import java.util.Calendar;
import java.util.Date;
public class TestLoop {
public static void main(String s[]) {
long start, end;
int[] a = new int[1000000];
Calendar cal = Calendar.getInstance();
start = System.currentTimeMillis();
for (int i = 0; i
Date dt = cal.getTime();
}
end = System.currentTimeMillis();
System.out.println(end – start + ” milli “
+ “seconds for Instantiating object out side Loop”);
start = System.currentTimeMillis();
TestName tname = null;
for (int j = 0; j
Date dt = Calendar.getInstance().getTime();
}
end = System.currentTimeMillis();
System.out.println(end – start + ” “
+ “milli seconds Instantiating object inside Loop “);
}
}
0 milli seconds for Instantiating object out side Loop
797 milli seconds Instantiating object inside Loop

Nested loop gives big impact on performance and some time it make worse if not controlled properly. Need to double think before using the nested loop and try to find some alternative way to handle the same. Even if it is used, it should not go to level three in nested loop.
It is explained in the below code.

public class TestLoop {
public static void main(String s[]) {
long start, end;
int[] a = new int[100000];
int[] b = new int[100000];
start = System.currentTimeMillis();
for (int i = 0; i
}
end = System.currentTimeMillis();
System.out.println(end – start + ” ” + “milli seconds for One Time Loop”);
start = System.currentTimeMillis();
for (int j = 0; j
for (int i = 0; i
}
end = System.currentTimeMillis();
System.out.println(end – start + ” ” + “milli seconds for loop B inside Loop A”);
}
}
Result:
0 milli seconds for One Time Loop
44015 milli seconds for loop B inside Loop A
You can see the above result how it becomes 44015 ms for executing the loop inside the loop. These are figure for just an empty loop. For any process getting invoked inside the nested loop, the time will be exorbitantly increase.. I would suggest you to think before using the nesting loop with large data and try to avoid as much as possible. You could try to change/write a code in such a way that it would minimize the nested loop. It is explained using the below code. In the below code I am trying to match the value in a big array and print the ‘Found match’ on the console.
public class TestLoop {
public static void main(String s[]) {
long start, end; String[] arrFirst = new String[1000000];
String[] arrSecond = { “0”, “1” };
for (int i = 0; i length; i++) {
arrFirst[i] = String.valueOf(i);
}
start = System.currentTimeMillis();
for (int i = 0; i length; i++) {
for (int j = 0; j length; j++) {
if (arrFirst[i].equalsIgnoreCase(arrSecond[j])) {
System.out.println(“Found match”);
}
}
}
end = System.currentTimeMillis();
System.out.println(end – start + ” milli “+ “seconds for “);
start = System.currentTimeMillis();
}
}
Result: 30 ms
As you can see that it iterate the 1000000*2 times to complete the process. Since we know arrSecond having only two values 0 and 1 therefore we could easily minimize the code using below way

public class TestLoop1 {
public static void main(String s[]) {
long start, end;
String[] arrFirst = new String[1000000];
String[] arrSecond = { “0”, “1” };
for (int i = 0; i length; i++) {
arrFirst[i] = String.valueOf(i);
}
start = System.currentTimeMillis();
for (int i = 0; i length; i++) {
if ((arrSecond[0].equalsIgnoreCase(arrFirst[i]))|| (arrSecond[1].equalsIgnoreCase(arrFirst[i]))) {
System.out.println(“Found match”);
}
}
end = System.currentTimeMillis();
System.out.println(end – start + ” milli “+ “seconds for loop”);
}
}

Result: 15 ms

You could see it just iterate 1000000 times just half the above code and performance get improved twice.
I agree that this is not the best example but this would definitely provide you the way how to handle the nested loop