About "this" keyword in constructor

Question

Hi im new to java... Actually what is the use of "this" keyword? I have tried reference books and internet site still no prevail. As i see there are times when the constructor as
public hello(int number, number2){
n = number;
m = number2;
without this and some are
public hello(int number, number2){
this.number = number;
this.number2 = number2;
im so confused please help

Answer 1

It is a context reference keyword.
Basically, it is a safety word that tags a specific variable to a method or class.
In a class, you can have a member variable called aNumber. Now, in method, you could supply an argument that is also called aNumber. Example below:
public class MyClassExample {
    int aNumber;
    public MyClassExample(int aNumber) {
        aNumber = 1;
}In the above example, how does Java know what 'aNumber' I am refering to? The class member variable (global variable) or to the method argument variable (local variable)?
The "this" keyword marks the context to which we refer. If we wanted to tell Java to use the value of the method's argument as the value for our class variable, we would do (this):
public MyClassExample(int aNumber) {
    aNumber = this.aNumber;
}Now, what does this really do? Well, Java transparently switches the context for us, but this time we define it.
When we use the variable name, Java actually records the full context of "MyClassExample.aNumber" with the "MyClassExample.MyClassExample.aNumber"
See, I bet you never knew that!
What happens if we want it the other way around, then change which object to place the this keyword to.