构造器

 

 

子类是不继承父类的构造器（构造方法或者构造函数）的，它只是调用（隐式或显式）。

 

如果父类的构造器带有参数，则必须在子类的构造器中显式地通过 super 关键字调用父类的构造器并配以适当的参数列表。

 

如果父类构造器没有参数，则在子类的构造器中不需要使用 super 关键字调用父类构造器，系统会自动调用父类的无参构造器。

 

 

 

 

class SuperClass {
  private int n;
  SuperClass(){
    System.out.println("SuperClass()");
  }
  SuperClass(int n) {
    System.out.println("SuperClass(int n)");
    this.n = n;
  }
}


// SubClass 类继承
class SubClass extends SuperClass{
  private int n;
  
  SubClass(){ // 自动调用父类的无参数构造器
    System.out.println("SubClass");
  }  
  
  public SubClass(int n){ 
    super(300);  // 调用父类中带有参数的构造器
    System.out.println("SubClass(int n):"+n);
    this.n = n;
  }
}


// SubClass2 类继承
class SubClass2 extends SuperClass{
  private int n;
  
  SubClass2(){
    super(300);  // 调用父类中带有参数的构造器
    System.out.println("SubClass2");
  }  
  
  public SubClass2(int n){ // 自动调用父类的无参数构造器
    System.out.println("SubClass2(int n):"+n);
    this.n = n;
  }
}



public class TestSuperSub{
  public static void main (String args[]){
    System.out.println("------SubClass 类继承------");
    SubClass sc1 = new SubClass();
    SubClass sc2 = new SubClass(100); 
    System.out.println("------SubClass2 类继承------");
    SubClass2 sc3 = new SubClass2();
    SubClass2 sc4 = new SubClass2(200); 
  }
}

　　

 

class SuperClass
{
    private int n;

    SuperClass()
    {
        System.out.println("SuperClass()");
    }

    SuperClass(int n)
    {
        System.out.println("SuperClass(int n)");
        this.n = n;
    }
}

class SubClass extends SuperClass
{
    private int n;

    SubClass()
    {
        System.out.println("SubClass");
    }

    public SubClass(int n)
    {
        super(300);

        System.out.println("SubClass(int n):"+n);

        this.n = n;
    }
}

class SubClass2 extends SuperClass
{
    private int n;

    SubClass2()
    {
        super(300);
        System.out.println("SubClass2");
    }

    public SubClass2(int n)
    {
        System.out.println("SubClass2(int n):"+n);
        this.n = n;
    }
}

public class TestSuperSub
{
    public static void main (String args[])
  {
        System.out.println("-------------------------");
        SubClass sc1 = new SubClass();
        System.out.println("-----------------");
        SubClass sc2 = new SubClass(100);

        System.out.println("-----------------------------------------");

        System.out.println("-----------------------------------");
        SubClass2 sc3 = new SubClass2();
        System.out.println("-------------------------------");
        SubClass2 sc4 = new SubClass2(200);
    }
}