泛型的使⽤练习题题⽬要求：
Dao泛型类：
private Map<String,T> map = new HashMap<>(); //保存T类型的对象到map成员变量中
public void save(String id,T entity){
map.put(id,entity);
}
//从map中获得id对应的对象
public T get(String id){
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(id);
}
//替换map中key为id的内容，改为entity对象
public void update(String id,T entity){
if (ainsKey(id)){
map.put(id,entity);
}
}
//返回map中存放的所有的T对象
public List<T> list(){
//错误的:
//Collection<T> values = map.values();
//return (List<T>) values;
//正确的;
List<T> list = new ArrayList<>();
Collection<T> values = map.values();
for (T t : values){
list.add(t);
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return list;
}
//删除指定id对象
public void delete(String id){
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}
}
Ur 类：
private int id;
private int age;
private String name;
public Ur() {
}
public Ur(int id, int age, String name) { this.id = id;
this.age = age;
this.name = name;
}
@Override
public String toString() {
return "Ur{" +
"id=" + id +
", age=" + age +
", name='" + name + '\'' +
'}';
}
@Override
public int hashCode() {
return super.hashCode();
}
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@Override
public boolean equals(Object obj) {
return super.equals(obj);
}
机箱电源线public int getId() {
return id;
}
public void tId(int id) {
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public int getAge() {
return age;
}
public void tAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
放假表public void tName(String name) {
this.name = name;
}
}
测试类：
public static void main(String[] args) {
Dao<Ur> dao = new Dao<>();
dao.save("1001",new Ur(101,34,"周杰伦")); dao.save("1002",new Ur(102,35,"琨林")); dao.save("1003",new Ur(103,64,"蔡依林")); dao.update("1003",new Ur(104,30,"反就")); List<Ur> list = dao.list();
list.forEach(System.out::println);
}
}
