Java基础之泛型上限的体现

浅浅的花香味﹌ 2022-12-10 08:39 193阅读 0赞

package cn.itcast.p5.generic.advance.demo;
    
    import java.util.ArrayList;
    
    import cn.itcast.p2.bean.Person;
    import cn.itcast.p2.bean.Student;
    import cn.itcast.p2.bean.Worker;
    
    public class GenericAdvanceDemo3 {
        
    
    	/**
    	 * @param args
    	 */
    	public static void main(String[] args) {
        
    
    		ArrayList<Person> al1 = new ArrayList<Person>();
    		
    		al1.add(new Person("abc",30));
    		al1.add(new Person("abc4",34));
    		
    		ArrayList<Student> al2 = new ArrayList<Student>();
    		
    		al2.add(new Student("stu1",11));
    		al2.add(new Student("stu2",22));
    		
    		
    		ArrayList<Worker> al3 = new ArrayList<Worker>();
    		
    		al3.add(new Worker("stu1",11));
    		al3.add(new Worker("stu2",22));
    		
    		ArrayList<String> al4 = new ArrayList<String>();
    		al4.add("abcdeef");
    //		al1.addAll(al4);//错误，类型不匹配。
    		
    		al1.addAll(al2);
    		al1.addAll(al3);
    		
    		System.out.println(al1.size());
    		
    		
    //		printCollection(al2);
    //		printCollection(al);
    	}
    	
    	
    
    }
    
    /*
     * 一般在存储元素的时候都是用上限，因为这样取出都是按照上限类型来运算的。不会出现类型安全隐患。 
     * 
     */
    
    class MyCollection<E>{
        
    	public void add(E e){
        
    	
    	}
    	public void addAll(MyCollection<? extends E> e){
        
    		
    	}
    }

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