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Java????????????

???Java??????????????????????????????????????????????????????????????????????Java??????

????????

????Java?????????ArrayList???Object???????????????????????????????

?????????Java????????????????????????????????????????????????????

Java???????

Java??????????????

??????

?????????????

class MyClass
   
     {
    public void add(T str) {
        // T??????????????????????T??
    }
}
   

????????

MyClass
   
     mc = new MyClass<>();
mc.add("abc"); // ??
MyClass
    
      mc2 = new MyClass<>();
mc2.add(1); // ??
    
   

???????

????????????

interface MyInter {
    void add(Q q);
}
class MyClass01 implements MyInter {
    @Override
    public void add(Q q) {
        // q??????MyInter??
    }
}
class MyClass02 implements MyInter
       
         {
    @Override
    public void add(String s) {
        // s??????String
    }
}
       

???????

????????????

public class MyClass03 {
    public static 
 void method00(ArrayList
 list) {
        // list??????P???????
    }
}
// ?????
MyClass03.method00(new ArrayList
    
     ());
MyClass03.method00(new ArrayList
     
      ());
     
    

??????extends?super

???????extends?super????????????????????

class Fu {}
class Zi extends Fu {}
class Sun extends Zi {}
// ????? extends ??????
ArrayList
    fuList = new ArrayList<>();
fuList.add(new Fu());
fuList.add(new Zi()); // ?????Zi?Fu???
fuList.add(new Sun()); // ??

super???????

ArrayList
    superList = new ArrayList<>();
superList.add(new Fu()); // ??
superList.add(new Zi()); // ?????Zi?Fu????`super`????????
superList.add(new Object()); // ?????Object?Fu???

Java Map?????

Java?Map?????????????????????

Map
   
    > map = new HashMap<>();
map.put("??", Arrays.asList("?????1", "?????2"));
map.put("??", Arrays.asList("?????1", "?????2"));
// ????????
Set
    
      keySet = map.keySet();
for (String zuZhang : keySet) {
    System.out.println(zuZhang);
}
// ????????
Collection
     
      
       > values = map.values();
for (List
       
         group : values) {
    System.out.println(group);
}
// ?????????
Set
        
         
          > entrySet = map.entrySet(); for (Map.Entry
          
           > entry : entrySet) { System.out.println(entry.getKey() + ": " + String.join(",", entry.getValue())); }
          
         
        
       
      
     
    
   

??

?????????????Java????????????????????????????????????????????????????????????????????????????