在之前的文章java反射-Method中分析了Method的执行过程,Constructor是特殊的Method,实现原理大同小异
- 代码
import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.lang.reflect.Constructor;
public class TestProxyConstructor {
private String name;
private int age;
public TestProxyConstructor(String name, int age) {
this.name = name;
this.age = age;
}
@Override
public String toString() {
return "TestProxyField{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
public static void main(String[] args) throws Exception {
RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
System.out.println("============" + runtimeMXBean.getName());
Constructor<TestProxyConstructor> constructor = TestProxyConstructor.class.getConstructor(new Class[]{String.class,int.class});
TestProxyConstructor testProxyConstructor = constructor.newInstance("hello world...",18);
System.out.println(testProxyConstructor);
}
}
执行结果
pid=12428
TestProxyField{name='hello world...', age=18}
- constructor.newInstance("hello world...",18);的执行如下,最后由ConstructorAccessor执行
@CallerSensitive
public T newInstance(Object ... initargs)
throws InstantiationException, IllegalAccessException,
IllegalArgumentException, InvocationTargetException
{
if (!override) {
if (!Reflection.quickCheckMemberAccess(clazz, modifiers)) {
Class<?> caller = Reflection.getCallerClass();
checkAccess(caller, clazz, null, modifiers);
}
}
if ((clazz.getModifiers() & Modifier.ENUM) != 0)
throw new IllegalArgumentException("Cannot reflectively create enum objects");
ConstructorAccessor ca = constructorAccessor; // read volatile
if (ca == null) {
ca = acquireConstructorAccessor();
}
@SuppressWarnings("unchecked")
T inst = (T) ca.newInstance(initargs);
return inst;
}
- 使用工具HDFS查看生成ConstructorAccessor,反编译后如下:
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//
package sun.reflect;
import java.lang.reflect.InvocationTargetException;
public class GeneratedConstructorAccessor8 extends ConstructorAccessorImpl {
public GeneratedConstructorAccessor8() {
}
public Object newInstance(Object[] var1) throws InvocationTargetException {
TestProxyConstructor var10000;
TestProxyConstructor var10001;
String var10002;
int var10003;
try {
var10000 = new TestProxyConstructor;
var10001 = var10000;
if(var1.length != 2) {
throw new IllegalArgumentException();
}
var10002 = (String)var1[0];
Object var2 = var1[1];
if(var2 instanceof Byte) {
var10003 = ((Byte)var2).byteValue();
} else if(var2 instanceof Character) {
var10003 = ((Character)var2).charValue();
} else if(var2 instanceof Short) {
var10003 = ((Short)var2).shortValue();
} else {
if(!(var2 instanceof Integer)) {
throw new IllegalArgumentException();
}
var10003 = ((Integer)var2).intValue();
}
} catch (NullPointerException | ClassCastException var4) {
throw new IllegalArgumentException(var4.toString());
}
try {
var10001.<init>(var10002, var10003);
return var10000;
} catch (Throwable var3) {
throw new InvocationTargetException(var3);
}
}
}
发现:其实我们平时new Object()这个操作不是原子性
