why do we use this keyword in java code example

Example: how to use the this keyword in java

class Other{
    public double num;
    public Other(int num){
        this.num = num;
        System.out.println(num);
      	//print 5 to the console
    }
}

class scratch{
    public static void main(String[] args) {
        Other method = new Other(5);
        System.out.println(method.num);
      	//prints 5.0 to the console
    }
}