Code Optimization : Effective Java Chapter 2 : Item 5 : Avoid Creating unnecessary Objects

Code Optimization : Effective Java Chapter 2 : Item 5 : Avoid Creating unnecessary objects

Reuse can be both faster and morestylish. An object can always be reused if it is immutable.
String s = "stringette";
This version uses a single String instance, rather than creating a new one each time it is executed.
In the below mentioned code we are creating date object inside the , and we should not do it that way since what will happen every time we will call the method the same object is being created, whereas a better approach will be to use the same DATE object. ```java

public class Person { private final Date birthDate; // Other fields, methods, and constructor omitted public boolean isBabyBoomer() { // Unnecessary allocation of expensive object

Calendar gmtCal = Calendar.getInstance(TimeZone.getTimeZone("GMT")); gmtCal.set(1946, Calendar.JANUARY, 1, 0, 0, 0);

Date boomStart = gmtCal.getTime();

gmtCal.set(1965, Calendar.JANUARY, 1, 0, 0, 0);

Date boomEnd = gmtCal.getTime();

return birthDate.compareTo(boomStart) >= 0 && birthDate.compareTo(boomEnd)<0;} }




- **Optmized way of the above class is** 
```java

class Person {
private final Date birthDate;
// Other fields, methods, and constructor omitted
/**
* The starting and ending dates of the baby boom.
*/
private static final Date BOOM_START;
private static final Date BOOM_END;

static {
Calendar gmtCal =
Calendar.getInstance(TimeZone.getTimeZone("GMT"));
gmtCal.set(1946, Calendar.JANUARY, 1, 0, 0, 0);
BOOM_START = gmtCal.getTime();
gmtCal.set(1965, Calendar.JANUARY, 1, 0, 0, 0);
BOOM_END = gmtCal.getTime();

}
public boolean isBabyBoomer() {
return birthDate.compareTo(BOOM_START) >= 0 &&
birthDate.compareTo(BOOM_END) < 0;
}
}

Prefer Primitive over autoboxed

Not so optmized code

// Hideously slow program! Can you spot the object creation?
public static void main(String[] args) {
Long sum = 0L;
for (long i = 0; i < Integer.MAX_VALUE; i++) {
sum += i;
}
System.out.println(sum);
}

above code will give correct answer and logic is also correct, but since we have used here Long instead of long so it will create
The variable sum is declared as a Long instead of a long, which means that the program constructs about 231 unnecessary Long instances (roughly one for each time the long i is added to the Long sum).

Code sample Not optimized

public class Improve {  
    public static void main(String[] args){  
      System.out.println("hello world");  

      long startTime=System.currentTimeMillis();  

      //find how much memory is taken by the program  

      Runtime runtime=Runtime.getRuntime();  
      long before,after;  
      System.gc();  

      before=runtime.freeMemory();  
      Long sum=0L;  
      for(long i=0 ; i< Integer.MAX_VALUE;i++) {  
          sum=sum+i;  
      }  

      after=runtime.freeMemory(); //it tells amount of free memory in jvm  
      System.out.println("Memory used "+ (before-after));   // this will be before-after : free memory will decrease right  

      long endTime=System.currentTimeMillis();  
      System.out.println("Time Taken "+ (endTime-startTime));  
      System.out.println(sum);  
    }  
}

Output

Memory used -48176240
Time Taken 6187    
2305843005992468481

After optimized code

just converted Long to long and there is vast improvemen in code it means improve memory usage improves performance

prefer primitives to boxed primitives, and watch out for unintentional autoboxing.

public class Improve {  
  public static void main(String[] args){  
    System.out.println("hello world");  

    long startTime=System.currentTimeMillis();  

    //find how much memory is taken by the program  

    Runtime runtime=Runtime.getRuntime();  
    long before,after;  
    System.gc();  

    before=runtime.freeMemory();  
    long sum=0L;  
    for(long i=0 ; i< Integer.MAX_VALUE;i++) {  
        sum=sum+i;  
    }  

    after=runtime.freeMemory(); //it tells amount of free memory in jvm  
    System.out.println("Memory used "+ (before-after));   // this will be before-after : free memory will decrease right  

    long endTime=System.currentTimeMillis();  
    System.out.println("Time Taken "+ (endTime-startTime));  
    System.out.println(sum);  
  }  
}

Output

Memory used 2663400
Time Taken 754
2305843005992468481