java.lang.reflect反射之 Constructor＜T＞

Constructor提供了一個類的單個構造函數的信息和訪問。

Constructor允許在將實際參數與newInstance（）與底層構造函數的形式參數進行匹配時進行擴展轉換，但如果發生縮小轉換，則拋出IllegalArgumentException�0�2。

方法摘要
�0�2
Modifier and Type Method and Description
boolean equals(Object�0�2obj)
Compares this�0�2Constructor�0�2against the specified object.

AnnotatedType getAnnotatedReceiverType()
Returns an�0�2AnnotatedType�0�2object that represents the use of a type to specify the receiver type of the method/constructor represented by this Executable object.

AnnotatedType getAnnotatedReturnType()
Returns an�0�2AnnotatedType�0�2object that represents the use of a type to specify the return type of the method/constructor represented by this Executable.

<T extends�0�2Annotation>
T getAnnotation(Class<T>�0�2annotationClass)
Returns this element's annotation for the specified type if such an annotation is�0�2present, else null.

Annotation[] getDeclaredAnnotations()
Returns annotations that are�0�2directly present�0�2on this element.

Class<T> getDeclaringClass()
Returns the�0�2Class�0�2object representing the class or interface that declares the executable represented by this object.

Class<?>[] getExceptionTypes()
Returns an array of�0�2Class�0�2objects that represent the types of exceptions declared to be thrown by the underlying executable represented by this object.

Type[] getGenericExceptionTypes()
Returns an array of�0�2Type�0�2objects that represent the exceptions declared to be thrown by this executable object.

Type[] getGenericParameterTypes()
Returns an array of�0�2Type�0�2objects that represent the formal parameter types, in declaration order, of the executable represented by this object.

int getModifiers()
Returns the Java language�0�2modifiers�0�2for the executable represented by this object.

String getName()
Returns the name of this constructor, as a string.

Annotation[][] getParameterAnnotations()
Returns an array of arrays of�0�2Annotations that represent the annotations on the formal parameters, in declaration order, of the�0�2Executable�0�2represented by this object.

int getParameterCount()
Returns the number of formal parameters (whether explicitly declared or implicitly declared or neither) for the executable represented by this object.

Class<?>[] getParameterTypes()
Returns an array of�0�2Class�0�2objects that represent the formal parameter types, in declaration order, of the executable represented by this object.

TypeVariable<Constructor<T>>[] getTypeParameters()
Returns an array of�0�2TypeVariable�0�2objects that represent the type variables declared by the generic declaration represented by this�0�2GenericDeclaration�0�2object, in declaration order.

int hashCode()
Returns a hashcode for this�0�2Constructor.

boolean isSynthetic()
Returns�0�2true�0�2if this executable is a synthetic construct; returns�0�2false�0�2otherwise.

boolean isVarArgs()
Returns�0�2true�0�2if this executable was declared to take a variable number of arguments; returns�0�2false�0�2otherwise.

T newInstance(Object...�0�2initargs)
Uses the constructor represented by this�0�2Constructor�0�2object to create and initialize a new instance of the constructor's declaring class, with the specified initialization parameters.

使用此Constructor對象表示的構造函數，使用指定的初始化參數來創建和初始化構造函數的聲明類的新實例。各個參數將自動解包以匹配原始形式參數，並且原始參數和引用參數都需要進行方法調用轉換。

如果基礎構造函數所需的形式參數數量爲0，則提供的initargs數組的長度可以爲0或爲null。

如果構造函數的聲明類是非靜態上下文中的內部類，則構造函數的第一個參數必須是封閉實例；

如果實際參數和形式參數的數量不同等因素，則會拋IllegalArgumentException異常

String toGenericString()
Returns a string describing this�0�2Constructor, including type parameters.

String toString()
Returns a string describing this�0�2Constructor.

示例

public class ConstructorDemo {
private Integer count;

public ConstructorDemo() {
    this.count = 10;
}

public ConstructorDemo(Integer count) {
    this.count = count;

}

private ConstructorDemo(Integer count, Integer count2) {
    this.count = count;

}

@Override
public String toString() {
    return "ConstructorDemo [count=" + count + "]";
}

public static void main(String[] args) throws InstantiationException, NoSuchMethodException, SecurityException,
        IllegalAccessException, IllegalArgumentException, InvocationTargetException {
    Constructor[] constructors = ConstructorDemo.class.getConstructors();
    for (Constructor constructor : constructors) {
        System.out.println(constructor.toString());
    }
    System.out.println("*******************************");
    constructors = ConstructorDemo.class.getDeclaredConstructors();
    for (Constructor constructor : constructors) {
        System.out.println(constructor.toString());
    }
    System.out.println("*******************************");
    Constructor constructor = ConstructorDemo.class.getConstructor(Integer.class);
    Constructor constructor2 = ConstructorDemo.class.getConstructor();
    Constructor constructor3 = ConstructorDemo.class.getDeclaredConstructor(Integer.class, Integer.class);
    System.out.println(ConstructorDemo.class.newInstance());
    System.out.println(constructor2.newInstance());
    System.out.println(constructor.newInstance(new Integer(100)));
    System.out.println(constructor3.newInstance(new Integer(100), new Integer(100)));
}

}
�0�2運行結果

public com.cignacmb.common.utils.ConstructorDemo(java.lang.Integer)
public com.cignacmb.common.utils.ConstructorDemo()

private com.cignacmb.common.utils.ConstructorDemo(java.lang.Integer,java.lang.Integer)
public com.cignacmb.common.utils.ConstructorDemo(java.lang.Integer)
public com.cignacmb.common.utils.ConstructorDemo()

ConstructorDemo [count=10]
ConstructorDemo [count=10]
ConstructorDemo [count=100]
ConstructorDemo [count=100]

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java.lang.reflect反射之 Constructor＜T＞

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