理解Java构造器中的"this"

Calling Another Constructor

if the first statement of a constructor has the form this(...), then the constructor calls another constructor of the same class. For example,

public Employee(double s)
{
    this("Employee #" + nextId, s);
    nextId++;
}

When you call `new Employee(60000), the `Employee(double)` constructor calls the `Employee(String, double)` constructor.

import java.util.*;

/*

• This program demonstrates object construction.
  
  */

public class ConstructorTest

{

public static void main(String[] args)

{

// fill the staff array with three Employee objects

Employee[] staff = new Employee[3];

staff[0] = new Employee("Harry", 40000);

staff[1] = new Employee(60000);

staff[2] = new Employee();

    //print out inofrmation about all Employee objects
    for(Employee anEmployee : staff)
    {
        System.out.println("name =" + anEmployee.getName() + ", id =" + anEmployee.getId() + ", salary="
        + anEmployee.getSalary());
    }

}

}

class Employee

{

private static int nextId;

private int id;
private String name = ""; //instance field initialization
private double salary;

//static initialization block
{
    Random generator = new Random();
    // set nextId to a random number between 0 and 9999
    nextId = generator.nextInt(10000);
}

// object initialization block

{
    id = nextId;
    nextId++;
}

// three overload constructors

public Employee(String n, double s)
{
    name = n;
    salary = s;
    System.out.println("Constructor: Employee(String n, double s) is called.");
}

public Employee(double s)
{
    // calls the Employee(String, doulbe)constructor
    this("Employee #" + nextId, s);

}

// the default constructor
public Employee()
{
    // name initialization to "" --see above
    // salary not explicitly set -- initialized to 0
    // id initialized in initialization block
    System.out.println("The default constructor Employee() is called.");
}

public String getName()
{
    return name;
}

public double getSalary()
{
    return salary;
}

public int getId()
{
    return id;
}

}

输出结果：

Constructor: Employee(String n, double s) is called.
Constructor: Employee(String n, double s) is called.
The default constructor Employee() is called.
Disconnected from the target VM, address: '127.0.0.1:36707', transport: 'socket'
name =Harry, id =257, salary=40000.0
name =Employee #258, id =4283, salary=60000.0
name =, id =2113, salary=0.0

Process finished with exit code 0