method.java

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/*
 * @(#)Method.java	1.36 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.lang.reflect;

import sun.reflect.MethodAccessor;
import sun.reflect.Reflection;

/**
 * A <code>Method</code> provides information about, and access to, a single method
 * on a class or interface.  The reflected method may be a class method
 * or an instance method (including an abstract method).
 *
 * <p>A <code>Method</code> permits widening conversions to occur when matching the
 * actual parameters to invokewith the underlying method's formal
 * parameters, but it throws an <code>IllegalArgumentException</code> if a
 * narrowing conversion would occur.
 *
 * @see Member
 * @see java.lang.Class
 * @see java.lang.Class#getMethods()
 * @see java.lang.Class#getMethod(String, Class[])
 * @see java.lang.Class#getDeclaredMethods()
 * @see java.lang.Class#getDeclaredMethod(String, Class[])
 *
 * @author Kenneth Russell
 * @author Nakul Saraiya
 */
public final
class Method extends AccessibleObject implements Member {

    private Class		clazz;
    private int			slot;
    // This is guaranteed to be interned by the VM in the 1.4
    // reflection implementation
    private String		name;
    private Class		returnType;
    private Class[]		parameterTypes;
    private Class[]		exceptionTypes;
    private int			modifiers;
    private volatile MethodAccessor methodAccessor;
    // For sharing of MethodAccessors. This branching structure is
    // currently only two levels deep (i.e., one root Method and
    // potentially many Method objects pointing to it.)
    private Method              root;

    // More complicated security check cache needed here than for
    // Class.newInstance() and Constructor.newInstance()
    private volatile Class      securityCheckTargetClassCache;

    /**
     * Package-private constructor used by ReflectAccess to enable
     * instantiation of these objects in Java code from the java.lang
     * package via sun.reflect.LangReflectAccess.
     */
    Method(Class declaringClass,
           String name,
           Class[] parameterTypes,
           Class returnType,
           Class[] checkedExceptions,
           int modifiers,
           int slot)
    {
        this.clazz = declaringClass;
        this.name = name;
        this.parameterTypes = parameterTypes;
        this.returnType = returnType;
        this.exceptionTypes = checkedExceptions;
        this.modifiers = modifiers;
        this.slot = slot;
    }

    /**
     * Package-private routine (exposed to java.lang.Class via
     * ReflectAccess) which returns a copy of this Method. The copy's
     * "root" field points to this Method.
     */
    Method copy() {
        // This routine enables sharing of MethodAccessor objects
        // among Method objects which refer to the same underlying
        // method in the VM. (All of this contortion is only necessary
        // because of the "accessibility" bit in AccessibleObject,
        // which implicitly requires that new java.lang.reflect
        // objects be fabricated for each reflective call on Class
        // objects.)
        Method res = new Method(clazz, name, parameterTypes, returnType,
                                exceptionTypes, modifiers, slot);
        res.root = this;
        // Might as well eagerly propagate this if already present
        res.methodAccessor = methodAccessor;
        return res;
    }

    /**
     * Returns the <code>Class</code> object representing the class or interface
     * that declares the method represented by this <code>Method</code> object.
     */
    public Class getDeclaringClass() {
	return clazz;
    }

    /**
     * Returns the name of the method represented by this <code>Method</code> 
     * object, as a <code>String</code>.
     */
    public String getName() {
	return name;
    }

    /**
     * Returns the Java language modifiers for the method represented
     * by this <code>Method</code> object, as an integer. The <code>Modifier</code> class should
     * be used to decode the modifiers.
     *
     * @see Modifier
     */
    public int getModifiers() {
	return modifiers;
    }

    /**
     * Returns a <code>Class</code> object that represents the formal return type
     * of the method represented by this <code>Method</code> object.
     * 
     * @return the return type for the method this object represents
     */
    public Class getReturnType() {
	return returnType;
    }

    /**
     * Returns an array of <code>Class</code> objects that represent the formal
     * parameter types, in declaration order, of the method
     * represented by this <code>Method</code> object.  Returns an array of length
     * 0 if the underlying method takes no parameters.
     * 
     * @return the parameter types for the method this object
     * represents
     */
    public Class[] getParameterTypes() {
	return copy(parameterTypes);
    }

    /**
     * Returns an array of <code>Class</code> objects that represent 
     * the types of the exceptions declared to be thrown
     * by the underlying method
     * represented by this <code>Method</code> object.  Returns an array of length
     * 0 if the method declares no exceptions in its <code>throws</code> clause.
     * 
     * @return the exception types declared as being thrown by the
     * method this object represents
     */
    public Class[] getExceptionTypes() {
	return copy(exceptionTypes);
    }

    /**
     * Compares this <code>Method</code> against the specified object.  Returns
     * true if the objects are the same.  Two <code>Methods</code> are the same if
     * they were declared by the same class and have the same name
     * and formal parameter types and return type.
     */
    public boolean equals(Object obj) {
	if (obj != null && obj instanceof Method) {
	    Method other = (Method)obj;
	    if ((getDeclaringClass() == other.getDeclaringClass())
		&& (getName() == other.getName())) {
		/* Avoid unnecessary cloning */
		Class[] params1 = parameterTypes;
		Class[] params2 = other.parameterTypes;
		if (params1.length == params2.length) {
		    for (int i = 0; i < params1.length; i++) {
			if (params1[i] != params2[i])
			    return false;
		    }
		    return true;
		}
	    }
	}
	return false;
    }

    /**
     * Returns a hashcode for this <code>Method</code>.  The hashcode is computed
     * as the exclusive-or of the hashcodes for the underlying
     * method's declaring class name and the method's name.
     */
    public int hashCode() {
	return getDeclaringClass().getName().hashCode() ^ getName().hashCode();
    }

    /**
     * Returns a string describing this <code>Method</code>.  The string is
     * formatted as the method access modifiers, if any, followed by
     * the method return type, followed by a space, followed by the
     * class declaring the method, followed by a period, followed by
     * the method name, followed by a parenthesized, comma-separated
     * list of the method's formal parameter types. If the method
     * throws checked exceptions, the parameter list is followed by a
     * space, followed by the word throws followed by a
     * comma-separated list of the thrown exception types.
     * For example:
     * <pre>
     *    public boolean java.lang.Object.equals(java.lang.Object)
     * </pre>
     *
     * <p>The access modifiers are placed in canonical order as
     * specified by "The Java Language Specification".  This is
     * <tt>public</tt>, <tt>protected</tt> or <tt>private</tt> first,
     * and then other modifiers in the following order:
     * <tt>abstract</tt>, <tt>static</tt>, <tt>final</tt>,
     * <tt>synchronized</tt> <tt>native</tt>.
     */
    public String toString() {
	try {
	    StringBuffer sb = new StringBuffer();
	    int mod = getModifiers();
	    if (mod != 0) {
		sb.append(Modifier.toString(mod) + " ");
	    }
	    sb.append(Field.getTypeName(getReturnType()) + " ");
	    sb.append(Field.getTypeName(getDeclaringClass()) + ".");
	    sb.append(getName() + "(");
	    Class[] params = parameterTypes; // avoid clone
	    for (int j = 0; j < params.length; j++) {
		sb.append(Field.getTypeName(params[j]));
		if (j < (params.length - 1))
		    sb.append(",");
	    }
	    sb.append(")");
	    Class[] exceptions = exceptionTypes; // avoid clone
	    if (exceptions.length > 0) {
		sb.append(" throws ");
		for (int k = 0; k < exceptions.length; k++) {
		    sb.append(exceptions[k].getName());
		    if (k < (exceptions.length - 1))
			sb.append(",");
		}
	    }
	    return sb.toString();
	} catch (Exception e) {
	    return "<" + e + ">";
	}
    }

    /**
     * Invokes the underlying method represented by this <code>Method</code> 
     * object, on the specified object with the specified parameters.
     * Individual parameters are automatically unwrapped to match
     * primitive formal parameters, and both primitive and reference
     * parameters are subject to method invocation conversions as
     * necessary.
     *
     * <p>If the underlying method is static, then the specified <code>obj</code> 
     * argument is ignored. It may be null.
     *
     * <p>If the number of formal parameters required by the underlying method is
     * 0, the supplied <code>args</code> array may be of length 0 or null.
     *
     * <p>If the underlying method is an instance method, it is invoked
     * using dynamic method lookup as documented in The Java Language
     * Specification, Second Edition, section 15.12.4.4; in particular,
     * overriding based on the runtime type of the target object will occur.
     *
     * <p>If the underlying method is static, the class that declared
     * the method is initialized if it has not already been initialized.
     *
     * <p>If the method completes normally, the value it returns is
     * returned to the caller of invoke; if the value has a primitive
     * type, it is first appropriately wrapped in an object. If the
     * underlying method return type is void, the invocation returns
     * null.
     *
     * @param obj  the object the underlying method is invoked from
     * @param args the arguments used for the method call
     * @return the result of dispatching the method represented by
     * this object on <code>obj</code> with parameters
     * <code>args</code>
     *
     * @exception IllegalAccessException    if this <code>Method</code> object
     *              enforces Java language access control and the underlying
     *              method is inaccessible.
     * @exception IllegalArgumentException  if the method is an
     *              instance method and the specified object argument
     *              is not an instance of the class or interface
     *              declaring the underlying method (or of a subclass
     *              or implementor thereof); if the number of actual
     *              and formal parameters differ; if an unwrapping
     *              conversion for primitive arguments fails; or if,
     *              after possible unwrapping, a parameter value
     *              cannot be converted to the corresponding formal
     *              parameter type by a method invocation conversion.
     * @exception InvocationTargetException if the underlying method
     *              throws an exception.
     * @exception NullPointerException      if the specified object is null
     *              and the method is an instance method.
     * @exception ExceptionInInitializerError if the initialization
     * provoked by this method fails.
     */
    public Object invoke(Object obj, Object[] args)
	throws IllegalAccessException, IllegalArgumentException,
           InvocationTargetException
    {
        if (!override) {
            if (!Reflection.quickCheckMemberAccess(clazz, modifiers)) {
                Class caller = Reflection.getCallerClass(1);
                Class targetClass = ((obj == null || !Modifier.isProtected(modifiers))
                                     ? clazz
                                     : obj.getClass());
                if (securityCheckCache != caller ||
                    targetClass != securityCheckTargetClassCache) {
                    Reflection.ensureMemberAccess(caller, clazz, obj, modifiers);
                    securityCheckCache = caller;
                    securityCheckTargetClassCache = targetClass;
                }
            }
        }
        if (methodAccessor == null) acquireMethodAccessor();
        return methodAccessor.invoke(obj, args);
    }

    // NOTE that there is no synchronization used here. It is correct
    // (though not efficient) to generate more than one MethodAccessor
    // for a given Method. However, avoiding synchronization will
    // probably make the implementation more scalable.
    private void acquireMethodAccessor() {
        // First check to see if one has been created yet, and take it
        // if so
        MethodAccessor tmp = null;
        if (root != null) tmp = root.getMethodAccessor();
        if (tmp != null) {
            methodAccessor = tmp;
            return;
        }
        // Otherwise fabricate one and propagate it up to the root
        tmp = reflectionFactory.newMethodAccessor(this);
        setMethodAccessor(tmp);
    }

    // Returns MethodAccessor for this Method object, not looking up
    // the chain to the root
    MethodAccessor getMethodAccessor() {
        return methodAccessor;
    }

    // Sets the MethodAccessor for this Method object and
    // (recursively) its root
    void setMethodAccessor(MethodAccessor accessor) {
        methodAccessor = accessor;
        // Propagate up
        if (root != null) {
            root.setMethodAccessor(accessor);
        }
    }

    /*
     * Avoid clone()
     */
    static Class[] copy(Class[] in) {
	int l = in.length;
	if (l == 0)
	    return in;
	Class[] out = new Class[l];
	for (int i = 0; i < l; i++)
	    out[i] = in[i];
	return out;
    }
}