To be null or not to be ?

Book myBook = getBookFromSomeWhere();
System.out.println("myBook: " + myBook);

if (myBook == null) {
    System.out.println("myBook is null");
}
else {
    System.out.println("myBook is not null");
}

Run it ! And that display :

myBook: null
myBook is not null

How is it possible ?

Hahaha.

It is because we have:

Book {
...

public String toString() {
    return "null";
}

Funny, isn't it ?

Constant++

// FYI: Constants is a class (not an interface)

if (ts != null && ts.getTs().intValue() == 1){
 nbPc = Constants.CONST1A;
 Constants.CONST1A = Constants.CONST1A + 1;

 nbPs = Constants.CONST1B;
 Constants.CONST1B = Constants.CONST1B + 1;
} else if (ts != null && ts.getTs().intValue() == 2){
 nbPc = Constants.CONST2A;
 Constants.CONST2A = Constants.CONST2A + 1;

 nbPs = Constants.CONST2B;
 Constants.CONST2B = Constants.CONST2B + 1;
} else if (ts != null && ts.getTs().intValue() == 3){
 nbPc = Constants.CONST3A;
 Constants.CONST3A = Constants.CONST3A + 1;

 nbPs = Constants.CONST3B;
 Constants.CONST3B = Constants.CONST3B + 1;
} else if (ts != null && ts.getTs().intValue() == 4){
 nbPc = Constants.CONST4A;
 Constants.CONST4A = Constants.CONST4A + 1;

 nbPs = Constants.CONST4B;
 Constants.CONST4B = Constants.CONST4B + 1;
}

Oh that ignominious code.
First, it appears that if some fields were in a Class named Constants, they will be final.
The ts variable can be tested different from null only once.
Use myVariable++ instead of myVariable = myVariable + 1
At last, the use of if-statement to compare ts.getTs().intValue() to an int is not the best technic.

No brackets !

Let's have:

if (condition)
    doSomething();

And later, add doOtherThing() method to the condition.

if (condition)
    doSomething();
    doOtherThing();

And later, it appends. Ooops. I forgot the brackets.
So, I don't know why it is not required in every languages, BUT you MUST always use brackets.

if (condition) {
    doSomething();
}

And then

if (condition) {
    doSomething();
    doOtherThing();
}

This time I didn't forget the brackets 8-))