what is the meaning of this java code

[proeser waikmen]

I have following java code segments,

class Test{
int a=100;
private int b=200;

public void print(){
System.out.println(a);
System.out.println(b);
}
public void setB(int b){this.b=b;} //what is this
public int getB(){return b;} // and this
}

class Demo{
public static void main(String args[]){
Test t1=new Test();
System.out.println(t1.a);
System.out.println(t1.getB());
t1.setB(1000);
System.out.println(t1.getB());
}
}

I have comment above code. how we can use this in java code

[Joseph Mokenela]

Welcome to the Ranch.

this

refers to the instance of the current object.

when you have the setter method as below

 public void setB(int b){this.b=b;} 

You are seting the value that is passed as the paramete to the instance variable b

The getter method below is simply returning the value of the instance variable.

public int getB(){return b;}

[Jesse Duncan]

Hello, and welcome to the Ranch! You can format your code by clicking the button that says "code" in the post editor, which will give you two tags: [code] and [/code]. Your code needs to go between these tags. There, that looks better  

class Test{
    int a=100;
    private int b=200;

    public void print(){
        System.out.println(a);
        System.out.println(b);
    }

    public void setB(int b){this.b=b;} //what is this
    public int getB(){return b;} // and this
}

class Demo{
    public static void main(String args[]){
        Test t1=new Test();
        System.out.println(t1.a);
        System.out.println(t1.getB());
        t1.setB(1000);
        System.out.println(t1.getB());
    }
} 

[Campbell Ritchie]

That code shows that fields not marked private are accessible from outwith their class. The field a can be changed from elsewhere, so it shows lack of encapsulation.
You have been told correctly what the setB() method does, but it hasn't been explained. Because you have a field and a parameter both with the same name, the parameter takes precedence. To make sure you are referring to the field rather than the parameter, you call the field this.b. As you know, this is a keyword meaning the current object.

And (again) welcome to the Ranch