1：通过无参构造实例化对象
package cn.itcast;
/*
* 通过无参构造实例化对象
* 通过Class类本身实例化对象，使用newInstance方法
* 需要注意的是：实例化类中存在一个无参构造的方法,如果不存在将无法实例化Person对象；
* 如果没有则报异常：InstantionException
* */
public class ClassDemo03 {
public static void main(String[] args) {
//创建Class对象
Class class1 = null;
try {
class1=Class. forName("cn.itcast.Person");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//声明Person对象
Person p1 = null;
//实例化Person对象
try {
p1 = (Person) class1.newInstance();
} catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System. out.println(p1);
p1.setName("小李");
p1.setAge(20);
p1.setSex('男');
System. out.println(p1);
}
}
打印结果：
Person [name=null, age=0,sex= ]
Person [name=小李, age=20, sex=男]
2：通过有参构造实例化对象
如果实例化类中确实没有无参构造，就需要明确地调用类中的构造方法，将参数传递进去之后就可以才可以实例化操作；
public final class Constructor<T>
extends AccessibleObject
implements GenericDeclaration, Member
操作步骤：
1：获取要实例化类的带参构造
Constructor<?> c2 = class1.getConstructor(String. class,int.class, char.class);
//获取全部的构造方法
Constructor[] c1 = class1.getConstructors();
for (Constructor getCon : c1) {
//输出的全是public方法
System. out.println(getCon);
}
打印：
public cn.itcast.Person()
public cn.itcast.Person(java.lang.String,int,char)
2：通过c1=newInstance(),实例化对象
代码展示：
package cn.itcast;
import java.lang.reflect.Constructor;
public class ClassDemo04 {
public static void main(String[] args) {
//创建Class对象
Class<?> class1 = null;
try {
class1=Class. forName("cn.itcast.Person");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//声明Person对象
Person p1 = null;
//获取全部的构造方法
Constructor[] c1 = class1.getConstructors();
for (Constructor getCon : c1) {
//输出的全是public方法
System. out.println(getCon);
// System.out.println(getCon.getName());
// System.out.println(getCon.getParameterTypes());
// System.out.println(getCon.getModifiers());
}
try{
//获取Person类中的带参构造
Constructor<?> c2 = class1.getConstructor(String.class ,int.class, char.class );
p1 = (Person) c2. newInstance("小张",24, '男');
} catch(Exception e){
e.printStackTrace();
}
System. out.println(p1);
}
}
package cn.itcast;
public class Person {
private String name;
private int age;
private char sex;
public Person() {
super();
}
public Person(String name, int age, char sex) {
super();
this.name = name;
this.age = age;
this.sex = sex;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public char getSex() {
return sex;
}
public void setSex(char sex) {
this.sex = sex;
}
public void eat()
{
System.out.println("吃了");
}
@Override
public String toString() {
return "Person [name=" + name + ", age=" + age + ", sex=" + sex + "]";
}
}