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25 package java.lang.constant;
26 
27 import java.lang.invoke.TypeDescriptor;
28 import java.util.stream.Stream;
29 
30 import sun.invoke.util.Wrapper;
31 
32 import static java.lang.constant.ConstantUtils.binaryToInternal;
33 import static java.lang.constant.ConstantUtils.dropLastChar;
34 import static java.lang.constant.ConstantUtils.internalToBinary;
35 import static java.lang.constant.ConstantUtils.validateMemberName;
36 import static java.util.Objects.requireNonNull;
37 import static java.util.stream.Collectors.joining;
38 
39 /**
40  * A <a href="package-summary.html#nominal">nominal descriptor</a> for a
41  * {@link Class} constant.
42  *
43  * <p>For common system types, including all the primitive types, there are
44  * predefined {@linkplain ClassDesc} constants in {@link ConstantDescs}.
45  * (The {@code java.lang.constant} APIs consider {@code void} to be a primitive type.)
46  * To create a {@linkplain ClassDesc} for a class or interface type, use {@link #of} or
47  * {@link #ofDescriptor(String)}; to create a {@linkplain ClassDesc} for an array
48  * type, use {@link #ofDescriptor(String)}, or first obtain a
49  * {@linkplain ClassDesc} for the component type and then call the {@link #arrayType()}
50  * or {@link #arrayType(int)} methods.
51  *
52  * @see ConstantDescs
53  *
54  * @since 12
55  */
56 public sealed interface ClassDesc
57         extends ConstantDesc,
58                 TypeDescriptor.OfField<ClassDesc>
59         permits PrimitiveClassDescImpl,
60                 ReferenceClassDescImpl {
61 
62     /**
63      * Returns a {@linkplain ClassDesc} for a class or interface type,
64      * given the name of the class or interface, such as {@code "java.lang.String"}.
65      * (To create a descriptor for an array type, either use {@link #ofDescriptor(String)}
66      * or {@link #arrayType()}; to create a descriptor for a primitive type, use
67      * {@link #ofDescriptor(String)} or use the predefined constants in
68      * {@link ConstantDescs}).
69      *
70      * @param name the fully qualified (dot-separated) binary class name
71      * @return a {@linkplain ClassDesc} describing the desired class
72      * @throws NullPointerException if the argument is {@code null}
73      * @throws IllegalArgumentException if the name string is not in the
74      * correct format
75      */
of(String name)76     static ClassDesc of(String name) {
77         ConstantUtils.validateBinaryClassName(requireNonNull(name));
78         return ClassDesc.ofDescriptor("L" + binaryToInternal(name) + ";");
79     }
80 
81     /**
82      * Returns a {@linkplain ClassDesc} for a class or interface type,
83      * given a package name and the unqualified (simple) name for the
84      * class or interface.
85      *
86      * @param packageName the package name (dot-separated); if the package
87      *                    name is the empty string, the class is considered to
88      *                    be in the unnamed package
89      * @param className the unqualified (simple) class name
90      * @return a {@linkplain ClassDesc} describing the desired class
91      * @throws NullPointerException if any argument is {@code null}
92      * @throws IllegalArgumentException if the package name or class name are
93      * not in the correct format
94      */
of(String packageName, String className)95     static ClassDesc of(String packageName, String className) {
96         ConstantUtils.validateBinaryClassName(requireNonNull(packageName));
97         if (packageName.isEmpty()) {
98             return of(className);
99         }
100         validateMemberName(requireNonNull(className), false);
101         return ofDescriptor("L" + binaryToInternal(packageName) +
102                 (packageName.length() > 0 ? "/" : "") + className + ";");
103     }
104 
105     /**
106      * Returns a {@linkplain ClassDesc} given a descriptor string for a class,
107      * interface, array, or primitive type.
108      *
109      * @apiNote
110      *
111      * A field type descriptor string for a non-array type is either
112      * a one-letter code corresponding to a primitive type
113      * ({@code "J", "I", "C", "S", "B", "D", "F", "Z", "V"}), or the letter {@code "L"}, followed
114      * by the fully qualified binary name of a class, followed by {@code ";"}.
115      * A field type descriptor for an array type is the character {@code "["}
116      * followed by the field descriptor for the component type.  Examples of
117      * valid type descriptor strings include {@code "Ljava/lang/String;"}, {@code "I"},
118      * {@code "[I"}, {@code "V"}, {@code "[Ljava/lang/String;"}, etc.
119      * See JVMS 4.3.2 ("Field Descriptors") for more detail.
120      *
121      * @param descriptor a field descriptor string
122      * @return a {@linkplain ClassDesc} describing the desired class
123      * @throws NullPointerException if the argument is {@code null}
124      * @throws IllegalArgumentException if the name string is not in the
125      * correct format
126      * @jvms 4.3.2 Field Descriptors
127      * @jvms 4.4.1 The CONSTANT_Class_info Structure
128      */
ofDescriptor(String descriptor)129     static ClassDesc ofDescriptor(String descriptor) {
130         requireNonNull(descriptor);
131         if (descriptor.isEmpty()) {
132             throw new IllegalArgumentException(
133                     "not a valid reference type descriptor: " + descriptor);
134         }
135         int depth = ConstantUtils.arrayDepth(descriptor);
136         if (depth > ConstantUtils.MAX_ARRAY_TYPE_DESC_DIMENSIONS) {
137             throw new IllegalArgumentException(
138                     "Cannot create an array type descriptor with more than " +
139                     ConstantUtils.MAX_ARRAY_TYPE_DESC_DIMENSIONS + " dimensions");
140         }
141         return (descriptor.length() == 1)
142                ? new PrimitiveClassDescImpl(descriptor)
143                : new ReferenceClassDescImpl(descriptor);
144     }
145 
146     /**
147      * Returns a {@linkplain ClassDesc} for an array type whose component type
148      * is described by this {@linkplain ClassDesc}.
149      *
150      * @return a {@linkplain ClassDesc} describing the array type
151      * @throws IllegalStateException if the resulting {@linkplain ClassDesc} would have an array rank of greater than 255
152      * @jvms 4.4.1 The CONSTANT_Class_info Structure
153      */
arrayType()154     default ClassDesc arrayType() {
155         int depth = ConstantUtils.arrayDepth(descriptorString());
156         if (depth >= ConstantUtils.MAX_ARRAY_TYPE_DESC_DIMENSIONS) {
157             throw new IllegalStateException(
158                     "Cannot create an array type descriptor with more than " +
159                     ConstantUtils.MAX_ARRAY_TYPE_DESC_DIMENSIONS + " dimensions");
160         }
161         return arrayType(1);
162     }
163 
164     /**
165      * Returns a {@linkplain ClassDesc} for an array type of the specified rank,
166      * whose component type is described by this {@linkplain ClassDesc}.
167      *
168      * @param rank the rank of the array
169      * @return a {@linkplain ClassDesc} describing the array type
170      * @throws IllegalArgumentException if the rank is less than or equal to zero or if the rank of the resulting array type is
171      * greater than 255
172      * @jvms 4.4.1 The CONSTANT_Class_info Structure
173      */
arrayType(int rank)174     default ClassDesc arrayType(int rank) {
175         int currentDepth = ConstantUtils.arrayDepth(descriptorString());
176         if (rank <= 0 || currentDepth + rank > ConstantUtils.MAX_ARRAY_TYPE_DESC_DIMENSIONS)
177             throw new IllegalArgumentException("rank: " + currentDepth + rank);
178         return ClassDesc.ofDescriptor("[".repeat(rank) + descriptorString());
179     }
180 
181     /**
182      * Returns a {@linkplain ClassDesc} for a nested class of the class or
183      * interface type described by this {@linkplain ClassDesc}.
184      *
185      * @apiNote
186      *
187      * Example: If descriptor {@code d} describes the class {@code java.util.Map}, a
188      * descriptor for the class {@code java.util.Map.Entry} could be obtained
189      * by {@code d.nested("Entry")}.
190      *
191      * @param nestedName the unqualified name of the nested class
192      * @return a {@linkplain ClassDesc} describing the nested class
193      * @throws NullPointerException if the argument is {@code null}
194      * @throws IllegalStateException if this {@linkplain ClassDesc} does not
195      * describe a class or interface type
196      * @throws IllegalArgumentException if the nested class name is invalid
197      */
nested(String nestedName)198     default ClassDesc nested(String nestedName) {
199         validateMemberName(nestedName, false);
200         if (!isClassOrInterface())
201             throw new IllegalStateException("Outer class is not a class or interface type");
202         return ClassDesc.ofDescriptor(dropLastChar(descriptorString()) + "$" + nestedName + ";");
203     }
204 
205     /**
206      * Returns a {@linkplain ClassDesc} for a nested class of the class or
207      * interface type described by this {@linkplain ClassDesc}.
208      *
209      * @param firstNestedName the unqualified name of the first level of nested class
210      * @param moreNestedNames the unqualified name(s) of the remaining levels of
211      *                       nested class
212      * @return a {@linkplain ClassDesc} describing the nested class
213      * @throws NullPointerException if any argument or its contents is {@code null}
214      * @throws IllegalStateException if this {@linkplain ClassDesc} does not
215      * describe a class or interface type
216      * @throws IllegalArgumentException if the nested class name is invalid
217      */
nested(String firstNestedName, String... moreNestedNames)218     default ClassDesc nested(String firstNestedName, String... moreNestedNames) {
219         if (!isClassOrInterface())
220             throw new IllegalStateException("Outer class is not a class or interface type");
221         validateMemberName(firstNestedName, false);
222         requireNonNull(moreNestedNames);
223         for (String addNestedNames : moreNestedNames) {
224             validateMemberName(addNestedNames, false);
225         }
226         return moreNestedNames.length == 0
227                ? nested(firstNestedName)
228                : nested(firstNestedName + Stream.of(moreNestedNames).collect(joining("$", "$", "")));
229     }
230 
231     /**
232      * Returns whether this {@linkplain ClassDesc} describes an array type.
233      *
234      * @return whether this {@linkplain ClassDesc} describes an array type
235      */
isArray()236     default boolean isArray() {
237         return descriptorString().startsWith("[");
238     }
239 
240     /**
241      * Returns whether this {@linkplain ClassDesc} describes a primitive type.
242      *
243      * @return whether this {@linkplain ClassDesc} describes a primitive type
244      */
isPrimitive()245     default boolean isPrimitive() {
246         return descriptorString().length() == 1;
247     }
248 
249     /**
250      * Returns whether this {@linkplain ClassDesc} describes a class or interface type.
251      *
252      * @return whether this {@linkplain ClassDesc} describes a class or interface type
253      */
isClassOrInterface()254     default boolean isClassOrInterface() {
255         return descriptorString().startsWith("L");
256     }
257 
258     /**
259      * Returns the component type of this {@linkplain ClassDesc}, if it describes
260      * an array type, or {@code null} otherwise.
261      *
262      * @return a {@linkplain ClassDesc} describing the component type, or {@code null}
263      * if this descriptor does not describe an array type
264      */
componentType()265     default ClassDesc componentType() {
266         return isArray() ? ClassDesc.ofDescriptor(descriptorString().substring(1)) : null;
267     }
268 
269     /**
270      * Returns the package name of this {@linkplain ClassDesc}, if it describes
271      * a class or interface type.
272      *
273      * @return the package name, or the empty string if the class is in the
274      * default package, or this {@linkplain ClassDesc} does not describe a class or interface type
275      */
packageName()276     default String packageName() {
277         if (!isClassOrInterface())
278             return "";
279         String className = internalToBinary(ConstantUtils.dropFirstAndLastChar(descriptorString()));
280         int index = className.lastIndexOf('.');
281         return (index == -1) ? "" : className.substring(0, index);
282     }
283 
284     /**
285      * Returns a human-readable name for the type described by this descriptor.
286      *
287      * @implSpec
288      * <p>The default implementation returns the simple name
289      * (e.g., {@code int}) for primitive types, the unqualified class name
290      * for class or interface types, or the display name of the component type
291      * suffixed with the appropriate number of {@code []} pairs for array types.
292      *
293      * @return the human-readable name
294      */
displayName()295     default String displayName() {
296         if (isPrimitive())
297             return Wrapper.forBasicType(descriptorString().charAt(0)).primitiveSimpleName();
298         else if (isClassOrInterface()) {
299             return descriptorString().substring(Math.max(1, descriptorString().lastIndexOf('/') + 1),
300                                                 descriptorString().length() - 1);
301         }
302         else if (isArray()) {
303             int depth = ConstantUtils.arrayDepth(descriptorString());
304             ClassDesc c = this;
305             for (int i=0; i<depth; i++)
306                 c = c.componentType();
307             return c.displayName() + "[]".repeat(depth);
308         }
309         else
310             throw new IllegalStateException(descriptorString());
311     }
312 
313     /**
314      * Returns a field type descriptor string for this type
315      *
316      * @return the descriptor string
317      * @jvms 4.3.2 Field Descriptors
318      */
descriptorString()319     String descriptorString();
320 
321     /**
322      * Compare the specified object with this descriptor for equality.  Returns
323      * {@code true} if and only if the specified object is also a
324      * {@linkplain ClassDesc} and both describe the same type.
325      *
326      * @param o the other object
327      * @return whether this descriptor is equal to the other object
328      */
equals(Object o)329     boolean equals(Object o);
330 }
331