创建单个对象时如何执行多个构造函数

Question

我想在创建单个对象时执行多个构造函数.例如,我有一个像这样的类定义 -

public class Prg
{
    public Prg()
    {
        System.out.println("In default constructor");
    }
    public Prg(int a)
    {
        System.out.println("In single parameter constructor");
    }
    public Prg(int b, int c)
    {
        System.out.println("In multiple parameter constructor");
    }
}

我试图通过以下代码实现它 -

public class Prg
{
    public Prg()
    {
        System.out.println("In default constructor");
    }
    public Prg(int a)
    {
        Prg();
        System.out.println("In single parameter constructor");
    }
    public Prg(int b, int c)
    {
        Prg(b);
        System.out.println("In multiple parameter constructor");
    }
    public static void main(String s[])
    {
        Prg obj = new Prg(10, 20);
    }
}

但在这种情况下,它会产生如下错误 -

Prg.java:11: error: cannot find symbol
            Prg();
            ^
  symbol:   method Prg()
  location: class Prg
Prg.java:16: error: cannot find symbol
            Prg(b);
            ^
  symbol:   method Prg(int)
  location: class Prg
2 errors

谢谢

Answer 1

使用this()而不是Prg()在构造函数中

Answer 2

用this而不是Prg

    public Prg()
    {
        System.out.println("In default constructor");
    }
    public Prg(int a)
    {
        this();
        System.out.println("In single parameter constructor");
    }
    public Prg(int b, int c)
    {
        this(b);
        System.out.println("In multiple parameter constructor");
    }

Answer 3

usethis关键字。完整运行代码如下

public class Prg
{
    public Prg()
    {
        System.out.println("In default constructor");
    }
    public Prg(int a)
    {
        this();
        System.out.println("In single parameter constructor");
    }
    public Prg(int b, int c)
    {
        //Prg obj = new Prg(10, 20);

this(b);        System.out.println("In multiple parameter constructor");
    }
    public static void main(String s[])
    {
        Prg obj = new Prg(10, 20);
    }
}