java反射-Constructor

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

1. 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}

2. 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;
    }

3. 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