Java Performance Tips

Using shift operator for faster division and multiplication

Multiplications
              12 * 2     = 12 << 1
              12 * 4     = 12 << 2
              12 * 8     = 12 << 3
              12 * 16   = 12 << 4
              12 * 32   = 12 << 5
              12 * 64   = 12 << 6
              12 * 128 = 12 << 7
              12 * 256 = 12 << 8
Divisions
             12 / 2     = 12 >> 1
             12 / 4     = 12 >> 2
             12 / 8     = 12 >> 3
             12 / 16   = 12 >> 4
             12 / 32   = 12 >> 5
             12 / 64   = 12 >> 6
             12 / 128 = 12 >> 7
             12 / 256 = 12 >> 8

Classpath

Setting the classpath

For example If I have the class
/home/user01/Test.java
/home/user01/f1/TestA .java
/home/user01/f2/TestB .java
/home/user01/f3/TestC .java

TestA {
     public void show() {
           System.out.println("Show from TestA");
     }
} 

TestB {
     public void show() {
           System.out.println("Show from TestB");
     }
}


TestC {
     public void show() {
           System.out.println("Show from TestC");
     }
}

Test {
     public static void main(Stirng atr[]) {
               TestA ta = new TestA();
               TestB tb = new TestB();
               TestC tc = new TestC();
               ta.show();
               tb.show();
               tc.show();

     }
}

If each class reside in different folder we need to set the classpath for all the file, then only the file got compile

[user01@localhost user01] java Test.java
the above command will lead you with error messages

Test.java4: cannot find symbol
symbol : class TestB
location: class TestB
...................

To Compile the above class
javac -classpath /home/user01/f1:/home/user01/f2:/home/user01/f3 Test.java
To Execute the above class
java -classpath /home/user01/f1:/home/user01/f2:/home/user01/f3 Test