Java基础之泛型下限的体现

小鱼儿 2022-12-10 08:39 292阅读 0赞

package cn.itcast.p5.generic.advance.demo;
    
    import java.util.Comparator;
    import java.util.Iterator;
    import java.util.TreeSet;
    
    import cn.itcast.p2.bean.Person;
    import cn.itcast.p2.bean.Student;
    import cn.itcast.p2.bean.Worker;
    
    public class GenericAdvanceDemo4 {
        
    
    	/**
    	 * @param args
    	 */
    	public static void main(String[] args) {
        
    
    		TreeSet<Person> al1 = new TreeSet<Person>(new CompByName());
    		
    		al1.add(new Person("abc4",34));
    		al1.add(new Person("abc1",30));
    		al1.add(new Person("abc2",38));
    		
    		TreeSet<Student> al2 = new TreeSet<Student>(new CompByName());
    		
    		al2.add(new Student("stu1",11));
    		al2.add(new Student("stu7",20));
    		al2.add(new Student("stu2",22));
    		
    		
    		TreeSet<Worker> al3 = new TreeSet<Worker>();
    		
    		al3.add(new Worker("stu1",11));
    		al3.add(new Worker("stu2",22));
    		
    		TreeSet<String> al4 = new TreeSet<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());
    		
    		
    		
    		Iterator<Student> it = al2.iterator();
    		while(it.hasNext()){
        
    			System.out.println(it.next());
    		}
    		
    	}
    }
    
    
    /*
     * class TreeSet<Worker>
     * {
     * 		Tree(Comparator<? super Worker> comp);
     * }
     * 
     * 什么时候用下限呢？通常对集合中的元素进行取出操作时，可以是用下限。
     * 
     */
    
    class CompByName implements Comparator<Person>{
        
    
    	@Override
    	public int compare(Person o1, Person o2) {
        
    		
    		int temp = o1.getName().compareTo(o2.getName());
    		
    		return temp==0? o1.getAge()-o2.getAge():temp;
    	}
    	
    }
    
    class CompByStuName implements Comparator<Student>{
        
    
    	@Override
    	public int compare(Student o1, Student o2) {
        
    		
    		int temp = o1.getName().compareTo(o2.getName());
    		
    		return temp==0? o1.getAge()-o2.getAge():temp;
    	}
    	
    }
    
    class CompByWorkerName implements Comparator<Worker>{
        
    
    	@Override
    	public int compare(Worker o1, Worker o2) {
        
    		
    		int temp = o1.getName().compareTo(o2.getName());
    		
    		return temp==0? o1.getAge()-o2.getAge():temp;
    	}
    	
    }

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