Java tutorial
// ASM: a very small and fast Java bytecode manipulation framework // Copyright (c) 2000-2011 INRIA, France Telecom // All rights reserved. // // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions // are met: // 1. Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // 2. Redistributions in binary form must reproduce the above copyright // notice, this list of conditions and the following disclaimer in the // documentation and/or other materials provided with the distribution. // 3. Neither the name of the copyright holders nor the names of its // contributors may be used to endorse or promote products derived from // this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE // ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE // LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR // CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF // SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN // CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF // THE POSSIBILITY OF SUCH DAMAGE. package org.objectweb.asm.signature; import org.objectweb.asm.Opcodes; /** * A SignatureVisitor that generates signature literals, as defined in the Java Virtual Machine * Specification (JVMS). * * @see <a href="https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.9.1">JVMS * 4.7.9.1</a> * @author Thomas Hallgren * @author Eric Bruneton */ public class SignatureWriter extends SignatureVisitor { /** The builder used to construct the visited signature. */ private final StringBuilder stringBuilder = new StringBuilder(); /** Whether the visited signature contains formal type parameters. */ private boolean hasFormals; /** Whether the visited signature contains method parameter types. */ private boolean hasParameters; /** * The stack used to keep track of class types that have arguments. Each element of this stack is * a boolean encoded in one bit. The top of the stack is the least significant bit. Pushing false * = *2, pushing true = *2+1, popping = /2. * * <p>Class type arguments must be surrounded with '<' and '>' and, because * * <ol> * <li>class types can be nested (because type arguments can themselves be class types), * <li>SignatureWriter always returns 'this' in each visit* method (to avoid allocating new * SignatureWriter instances), * </ol> * * <p>we need a stack to properly balance these 'parentheses'. A new element is pushed on this * stack for each new visited type, and popped when the visit of this type ends (either is * visitEnd, or because visitInnerClassType is called). */ private int argumentStack; /** Constructs a new {@link SignatureWriter}. */ public SignatureWriter() { super(Opcodes.ASM7); } // ----------------------------------------------------------------------------------------------- // Implementation of the SignatureVisitor interface // ----------------------------------------------------------------------------------------------- @Override public void visitFormalTypeParameter(final String name) { if (!hasFormals) { hasFormals = true; stringBuilder.append('<'); } stringBuilder.append(name); stringBuilder.append(':'); } @Override public SignatureVisitor visitClassBound() { return this; } @Override public SignatureVisitor visitInterfaceBound() { stringBuilder.append(':'); return this; } @Override public SignatureVisitor visitSuperclass() { endFormals(); return this; } @Override public SignatureVisitor visitInterface() { return this; } @Override public SignatureVisitor visitParameterType() { endFormals(); if (!hasParameters) { hasParameters = true; stringBuilder.append('('); } return this; } @Override public SignatureVisitor visitReturnType() { endFormals(); if (!hasParameters) { stringBuilder.append('('); } stringBuilder.append(')'); return this; } @Override public SignatureVisitor visitExceptionType() { stringBuilder.append('^'); return this; } @Override public void visitBaseType(final char descriptor) { stringBuilder.append(descriptor); } @Override public void visitTypeVariable(final String name) { stringBuilder.append('T'); stringBuilder.append(name); stringBuilder.append(';'); } @Override public SignatureVisitor visitArrayType() { stringBuilder.append('['); return this; } @Override public void visitClassType(final String name) { stringBuilder.append('L'); stringBuilder.append(name); // Pushes 'false' on the stack, meaning that this type does not have type arguments (as far as // we can tell at this point). argumentStack *= 2; } @Override public void visitInnerClassType(final String name) { endArguments(); stringBuilder.append('.'); stringBuilder.append(name); // Pushes 'false' on the stack, meaning that this type does not have type arguments (as far as // we can tell at this point). argumentStack *= 2; } @Override public void visitTypeArgument() { // If the top of the stack is 'false', this means we are visiting the first type argument of the // currently visited type. We therefore need to append a '<', and to replace the top stack // element with 'true' (meaning that the current type does have type arguments). if (argumentStack % 2 == 0) { argumentStack |= 1; stringBuilder.append('<'); } stringBuilder.append('*'); } @Override public SignatureVisitor visitTypeArgument(final char wildcard) { // If the top of the stack is 'false', this means we are visiting the first type argument of the // currently visited type. We therefore need to append a '<', and to replace the top stack // element with 'true' (meaning that the current type does have type arguments). if (argumentStack % 2 == 0) { argumentStack |= 1; stringBuilder.append('<'); } if (wildcard != '=') { stringBuilder.append(wildcard); } return this; } @Override public void visitEnd() { endArguments(); stringBuilder.append(';'); } /** * Returns the signature that was built by this signature writer. * * @return the signature that was built by this signature writer. */ @Override public String toString() { return stringBuilder.toString(); } // ----------------------------------------------------------------------------------------------- // Utility methods // ----------------------------------------------------------------------------------------------- /** Ends the formal type parameters section of the signature. */ private void endFormals() { if (hasFormals) { hasFormals = false; stringBuilder.append('>'); } } /** Ends the type arguments of a class or inner class type. */ private void endArguments() { // If the top of the stack is 'true', this means that some type arguments have been visited for // the type whose visit is now ending. We therefore need to append a '>', and to pop one element // from the stack. if (argumentStack % 2 == 1) { stringBuilder.append('>'); } argumentStack /= 2; } }