Constructors

1. 构造函数是一种特殊的方法，和class有相同的名字
2. 构造函数是用来初始化类的实例变量的
3. 构造函数有两种类型：默认的构造函数和参数化的构造函数

ØConstructor is a special method that has the same name as that of a class

ØThe constructor is used to initialize the instance variables of the class 

ØTypes of  constructors:

§Default constructor

§Parameterized constructor

 

Parameterized constructor will be discussed along with method overloading

Default Constructor

ØIf the programmer does not code the constructor explicitly, the system provides a default constructor

§This initializes the instance variables to their default values

ØProgrammer can redefine the default constructor

§Such a constructor does not take any arguments

§The instance variables can be initialized by the user explicitly inside this constructor

 

Retail Application – Case Study

class Customer{

  private int customerId;

  public int getCustomerId(){

  return customerId;

  }

}

class Retail{

public static void main(String args[]){

  Customer custObj=new Customer();

  System.out.println("Customer Id:"+

  custObj.getCustomerId());

}

}

Output:

  Customer Id: 0

Note that the system provides a default constructor

 

class Customer{

  private int customerId;

  public Customer(){

  customerId=1000;

  }

  public int getCustomerId(){

  return customerId;

  }

}

class Retail{

public static void main(String args[]){

  Customer custObj=new Customer();

  System.out.println("Customer Id:“+  custObj.getCustomerId());

  }

}

Retail Application – Case Study 

class Customer{

  private int customerId;

  public Customer(){

  customerId=1000;

  }

  public int getCustomerId(){

  return customerId;

  }

}

class Retail{

public static void main(String args[]){

  Customer custObj=new Customer();

  System.out.println("Customer Id:“+  custObj.getCustomerId());

  }

}

Output:

  Customer Id: 1000

Note that the default constructor is redefined