继承中的构造方法和super关键字

清疚 2022-04-06 08:55 221阅读 0赞

# 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
    	
    	}
    }