Code States BE 부트캠프 #10

INDEX

1. Constructor

2. Inner Class

1. Constructor

A Constrcutor is the method that initialize the instance variables when the class is instantiated. Whent a class is instantiated with "new" keyword, a constructor initialize instance variables; there are several essential rules for constructor.

• 1. The name of constructor must be same to the className.

• 2. A constructor has NO RETURN TYPE and NO VOID keyword also.

     ClassName(parameter){...}

• 3. A constructor also cane be overloaded with different parameters.
• 4. If the developer doesn't make a Default Constructor(No parameters), Java compiler automatically makes one default constrctor when the instance of the class is made.
• 5. Constructor Overloading makes it possible to use same Class in various ways with various variables without making new variable everytime making new instances.

• this vs this()

this(): In a constructor, overloaded constructors can be called out with the method, this().

class Ex {
	public Ex() {
    System.out.println("the first constructor!")
    }
    
    public Ex(int x) {
    this(); 
    // this() methods that copies the default constructor in the overloaded second constructor.
    System.out.println("the second constructor!")
	    }
}
	

• this() method must be used only in a constructor
• this() method must be located the first line in a constructor.

this keyoword:

this keywords make it possible to use both the variables and parameters, which have same names, together with distingushing them in the constructors and methods: in the constructors and methods this. refers to the parameter in themselves.

• This keyword refers to the instance(Object) itself: <this.parameterName = ...;>
• It is generally used to distinguish instance field and local variables(or parameters), which have same name.

2. Inner Class

Inner Class is the class that is made inside of a class, which is only used when the outer calss and inner class are related, to reduce the complexity of codes.