Detailed explanation of obtaining objects through Class class

The way to obtain an object through the Class object is to obtain it through class.newInstance(), and instantiate an object by calling the default construction parameters.

 1 /** 2  * Created by hunt on 2017/6/27.   
 * 测试的实体类 4  
 * @Data 编译后会自动生成set、get、无惨构造、equals、canEqual、hashCode、toString方法 5  
 */ 6 @Data 7 public class Person { 8     private String name; 9     
 private int age;10 }

 1 /** 2  * Created by hunt on 2017/6/27. 3  
 */ 4 public class NewInstanceTest { 5     public static void main(String[] args) { 6         
 Class<Person> personClass = Person.class;//获取Class实例 7         try { 8             
 Person p = personClass.newInstance();//通过Class获得Person实例 9             
 p.setAge(28);10             p.setName("hunt");11             
 System.out.println(p);12         } catch (InstantiationException e) {13             
 e.printStackTrace();14         } catch (IllegalAccessException e) {15             
 e.printStackTrace();16         }17     }18 }

Tip: class.newInstance() is instantiated through a parameterless constructor. An object has a parameterless constructor by default. Parametric constructor, if there is a parameterized constructor, the parameterless constructor does not exist, and a java.lang.InstantiationException exception will be thrown when the object is obtained through reflection.

 1 /** 2  * Created by hunt on 2017/6/27. 3  
 * 测试的实体类 4  */ 5  6 public class Person { 7     private String name; 8     
 private int age; 9 10     public String getName() {11         return name;12     }13 14     
 public int getAge() {15         return age;16     }17 18     public void setName(String name) {19         
 this.name = name;20     }21 22     public void setAge(int age) {23         this.age = age;24     }25 26     
 public Person(String name,int age){}//有参数构造函数27 }

 1 /** 2  * Created by hunt on 2017/6/27. 3  */ 4 public class NewInstanceTest { 5     
 public static void main(String[] args) { 6         Class<Person> personClass = Person.class;//获取Class实例 7         
 try { 8             Person p = personClass.newInstance();//通过Class获得Person实例 9            
  p.setAge(28);10             
 p.setName("hunt");11             System.out.println(p.getAge()+"----"+p.getName());12         } 
 catch (InstantiationException e) {13             e.printStackTrace();14         } 
 catch (IllegalAccessException e) {15             e.printStackTrace();16         }     }
  }

Summary: When creating entity classes in the future, you must bring a no-argument constructor so that you can use reflection in the future. No exception is thrown when instantiating the object.

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