Using this keyword...Help

Question

Using this with a Field
The most common reason for using the this keyword is because a field is shadowed by a method or constructor parameter.
For example, the Point class was written like this
public class Point {
    public int x = 0;
    public int y = 0;
//constructor
public Point(int a, int b) {
    x = a;
    y = b;
}
}
but it could have been written like this:
public class Point {
    public int x = 0;
    public int y = 0;
//constructor
public Point(int x, int y) {
    this.x = x;
    this.y = y;
}
}
Each argument to the constructor shadows one of the object's fields — inside the constructor x is a local copy of the constructor's first argument. To refer to the Point field x, the constructor must use this.x.
This is from Oracle...
Can someone explain this for me?

Alexander Nikiforov · Answer

Well this keyword is just used for clarification. Use can use this for the first example.
```java
public class Point { 
  public int x = 0; 
  public int y = 0;
 //constructor
  public Point(int a, int b) {
    // assign to member "x" the value of argument "a"
    // straighforward
    this.x = a;
    this.y = b;
  }
}
```
The task that you are trying to achieve is to assign to member of the class the value of variable passed as argument
In the first case, you assign value of "a" to "x", which is member
But in the second case
```java
public class Point { 
  public int x = 0; 
  public int y = 0;
 //constructor
  public Point(int x, int x) {
    // compiler will be stumped
    // assign to member "x" the value of argument "x"
    // or assign to argument "x" the value of member "x" of this class
    x = x;
    y = x;
  }
}
```
Without this, no one knows what do you want to do : ?
- Do you want to assign to member "x" of the class value of the argument method "x"
- OR do you want to assign to argument of the method "x" value of the member "x"
It is simply hard to explain. 
this keyword is used for clarification for people and computer.
And I don't know a person that can interpret x=x line without additional information.

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Using this keyword...Help

1 Answer

Alexander Nikiforov

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Taebin You

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Alexander Nikiforov

Alexander Nikiforov