继承中的构造方法和super关键字

继承中的构造方法——super关键字

TestSuperSub.java

//继承中的构造方法——super关键字
class SuperClass {
    private int n;
  	
    SuperClass() {
        System.out.println("父类无参构造方法SuperClass()");
    }
    
    SuperClass(int n) {
        System.out.println("父类有参构造方法SuperClass(" + n + ")");
        this.n = n;
    }
}

class SubClass extends SuperClass {
    private int n;    
	//子类的构造过程必须调用其父类（基类）的构造方法
    SubClass(int n) {
		/*
		如果调用super必须写在子类构造方法的第一行
		如果子类的构造方法中没有显示的调用父类的构造方法，则默认调用基类的无参构造方法
		如果子类的构造方法中既没有显示调用父类的构造方法，父类也没有无参构造方法，则编译出错
		*/
    	//super();		
        System.out.println("子类有参构造方法SubClass(" + n + ")");
        this.n = n;
    }    
    SubClass() {
    	super(300);
        System.out.println("子类无参构造方法SubClass()");
    }
}

public class TestSuperSub {
    public static void main(String arg[]) {
        //SubClass sc1 = new SubClass();
        SubClass sc2 = new SubClass(400);
    }
}

 

构造方法和一般成员方法在继承中的区别

Sub.java

//构造方法和一般成员方法在继承中的区别
class A {
	protected void print(String str) {
		System.out.println(str);		
	}
	A(){
		print("A()");
	}
	public void f() {		
		print("A:f()");
	}
}

class B extends A {
	B(){
		print("B()");
	}
	//重写A中的f()
	public void f() {		
		print("B:f()");j
	}
}

public class Sub {
	public static void main(String[] args) {
		B b = new B();
		b.f();
		/*
			结果：
			A()
			B()
			B:f()
			分析结果，体会构造方法和一般成员方法在继承中的区别
		*/
	}
	
}

 

简单的练习，使用super关键字，以及继承中的构造方法，方法的重写Override

TestPer.java

//简单的练习，使用super关键字，以及继承中的构造方法，方法的重写Override
class Person {
	private String name;	//姓名
	private String location;	//地址
	
	Person(String name) {
		this.name = name;
		location = "北京";
	}
	
	Person(String name, String location){
		this.name = name;
		this.location = location;
	}
	
	public String info() {
		return "name: " + name + ";location: " + location;
	}
}

class Student extends Person {	
	private String school;	//学校
	
	Student(String name, String school) {
		this(name,"北京",school);
	}
	
	Student(String n, String l, String s) {
		super(n,l);
		this.school = s;
	}
	//重写Override	info()方法
	public String info() {
		return super.info() + ";school: " + school;
	}
}

class Teacher extends Person {
	private String capital;	//职称
	
	Teacher(String name, String capital) {
		this(name, "广州", capital);
	}
	
	Teacher(String n, String l, String capital) {
		super(n, l);
		this.capital = capital;
	}
	
	public String info() {
		return super.info() + ";capital: " + capital;
	} 
}

public class TestPer {
	public static void main(String[] args) {
		Person p1 = new Person("A");
		Person p2 = new Person("B","上海");
		Student s1 = new Student("C","第一实验小学");
		Student s2 = new Student("D","武汉","第二实验小学");
		System.out.println(p1.info());	//name: A;location: 北京
		System.out.println(p2.info());	//name: B;location: 上海
		System.out.println(s1.info());	//name: C;location: 北京;school: 第一实验小学
		System.out.println(s2.info());	//name: D;location: 武汉;school: 第二实验小学
		
		Teacher t1 = new Teacher("E", "教授");
        System.out.println(t1.info());	//name: E;location: 广州;capital: 教授
	
	}
}