java-泛型的继承

目录

父类或接口中的泛型可以被子类继承

泛型继承的四种情况

1.全部继承

2.部分继承 

3.实现父类泛型 

4.不实现父类泛型

父类或接口中的泛型可以被子类继承

继承泛型类和泛型接口

class ExtendClass<T>{

}

----->

class SubClass<T> extends ExtendClass<T>{

}

---

interface TestInterface<T>{

}

----->

class SubClass2<T> implements  TestInterface<T>{

}

public class Demo {
	public static void main(String[] args) {
		
	}
}

class Father<T>{
	T t;
	public Father(T t) {
		this.t=t;
	}
}
interface TestInterface<E>{
	
}
class Child<T,E> extends Father<T> implements TestInterface<E>{

	public Child(T t) {
		super(t);
	}
}

泛型继承的四种情况

父类--> abstract class Father<T1,T2>{}  

1.全部继承

class Child<T1,T2,T2> extends Father<T1,T2>{} 

public class Demo {
	public static void main(String[] args) {
		Father<Integer,String> f=new Child<>(1,"2");
		//Child<Integer,String,Boolean> c=new Child<>(1,"2");   此行会报错
		Child<Integer,String,Boolean> c=new Child<>(1,true);	//正确，不会报错（T1，T3继承）
	}
}

class Father<T1,T2>{
	T1 t1;
	T2 t2;
	public Father(T1 t1, T2 t2) {
		
		this.t1 = t1;
		this.t2 = t2;
		System.out.println("t1的类型："+this.t1.getClass());
		System.out.println("t2的类型："+this.t2.getClass());
	}
	
}
 /*class Child<T1,T2,T3>extends Father<T1,T2>{

	public Child(T1 t1, T2 t2) {
		super(t1, t2);
		
	}
	
}*/
//T3继承

class Child<T1,T2,T3>extends Father<T1,T3>{

	public Child(T1 t1, T3 t2) {
		super(t1, t2);
		
	}
	
}

//运行结果
t1的类型：class java.lang.Integer
t2的类型：class java.lang.String
t1的类型：class java.lang.Integer
t2的类型：class java.lang.Boolean

2，部分继承 

calss Child<T1,A,B> extends Father<T1,String>{}

public class Demo {
	public static void main(String[] args) {
	
		Child<String,Byte,Boolean> c=new Child<>("1","2");	//第二三个泛型可以是任意类型，不影响
}
}
class Father<T1,T2>{
	T1 t1;
	T2 t2;
	public Father(T1 t1, T2 t2) {
		
		this.t1 = t1;
		this.t2 = t2;
		System.out.println("t1的类型："+this.t1.getClass());
		System.out.println("t2的类型："+this.t2.getClass());
	}
	
}

//T3继承

class Child<T1,T2,T3>extends Father<T1,String>{

	public Child(T1 t1, String t2) {
		super(t1, t2);
		
	}
	
}


//运行结果
t1的类型：class java.lang.String
t2的类型：class java.lang.String

3.实现父类泛型 

class Child<A,B> extends Father<Integer,String>{}

子类在继承父类的时候，将父类所有的泛型都实现了，这样子类就不会继承父类的泛型了，即使创建了泛型，也是子类独有的。

public class Demo {
	public static void main(String[] args) {

	//前面类型改变不影响结果
		Child<Boolean,Boolean,Boolean> c=new Child<>(1,"2");	
	}
}

class Father<T1,T2>{
	T1 t1;
	T2 t2;
	public Father(T1 t1, T2 t2) {
		
		this.t1 = t1;
		this.t2 = t2;
		System.out.println("t1的类型："+this.t1.getClass());
		System.out.println("t2的类型："+this.t2.getClass());
	}
	
}


class Child<T1,T2,T3>extends Father<Integer,String>{//把所有泛型实现,子类再多的泛型与父类无关

	public Child(Integer t1, String t2) {
		super(t1, t2);
		
	}
	
}


//运行结果
t1的类型：class java.lang.Integer
t2的类型：class java.lang.String

4.不实现父类泛型

class Child extends Father{}

忽略父类泛型，既不实现，也不继承；这样不会报错，但是父类所有泛型成员会默认为Object类型

public class Demo {
	public static void main(String[] args) {

	//前面类型改变不影响结果
		Child<Boolean,Boolean,Boolean> c=new Child<>("1","2");	//写什么都可以
		System.out.println("--");
		Child<Boolean,Boolean,Boolean> d=new Child<>(1,"2");	
	}
}

class Father<T1,T2>{
	T1 t1;
	T2 t2;
	public Father(T1 t1, T2 t2) {
		
		this.t1 = t1;
		this.t2 = t2;
		System.out.println("t1的类型："+this.t1.getClass());
		System.out.println("t2的类型："+this.t2.getClass());
	}
	
}


class Child<T1,T2,T3>extends Father{

	public Child(Object t1, Object t2) {
		super(t1, t2);
		// TODO 自动生成的构造函数存根
	}
}


//运行结果
t1的类型：class java.lang.String
t2的类型：class java.lang.String
--
t1的类型：class java.lang.Integer
t2的类型：class java.lang.String