eg. String s1 = new String("Java is cool");
String s2 = new String("Java is cool"); //(s1==s2 is false
but s1.equals(s2) true )

== is true means, .equals(Object o)ALSO true.

Is the above statement true? I can give an example for true

String s1 = new String("Java is cool");
String s2 = s1; //both == and equals(..) are true
If the ans is false Can anybody give a code example?
Because if 2 ref are same means , the object they both refer to must be same right? which means their contents shd be same.

My technique was to study topics in Java to my satisfaction, and then prepare for the exam. It took 8 months from complete start with no experience in OOP to finishing last Monday with 98% score.

As for the mock tests, I left them for almost the end and didn't repeat any for the reasons that you mention. I didn't take them all at once, but these are the ones: the two by Marcus Green, the two by Barry Boone in his Java 1.1 Certification book, all the exercises in the Roberts and Heller and all the exercises in JAVA 2 EXAM CRAM book plus the mock test the same day of the real exam.

Also, all applicable exercises in the Mughal and Rasmussen book. This book has applets and introductory Swing which are NOT in the exam.

I started Java last June, starting from no OOP experience as I said, but with a lot of experience in assembly language and C (not to be confused with C++).

I DID NOT STUDY FOR THE TEST for 8 months!. Only three, tops.

I did teach myself Java at my own pace and in more detail that the exam requires. In fact, I did not know nor care about Certification until about 5 months into my studies.

I then wrote a few Java applets and programs (which are available in ) not only to practice but one that I needed to display the HTTP header of any file on the public Web.

THEN I decided to look into Certification and for reasons that I am cutting short for brevity and which I have posted about before, I decided to go for Certification three months ago. I thought I knew my stuff and when I took the first questions of the Roberts and Heller book and failed more than a few of them, I figured that the test was not going to be easy and as such, possibly of some value after all.

if(eq.equals(eq1))
System.out.println("equals() works");
//none of the statements will get printed because equals //method is not overrided

}
}

code:

---

class Item
{
  private float value;
  // two Items are equal only if the values are the same
  //
  public boolean equals(Object other)
  {
    return (other instanceof Item) && (value == other.value);
  }
}

---

I have used this sort of idiom plenty of times, and I'm sure many people have. It seems very straightforward and reasonable. With integers, Strings etc. it works very well.

But beware It won't always work with floats and doubles. The reason is the peculiar behaviour of the NaN (not-a-number) value which all floats and double may contain. NaN is strange in that it is never equal to any other number, not even itself. So if an Item from the above class happens to contain NaN and is compared with itself, then == will be true (the addresses are the same) but equals will not.