src/java.base/share/classes/java/lang/classfile/attribute/ConstantValueAttribute.java

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package java.lang.classfile.attribute;

import java.lang.classfile.Attribute;
import java.lang.classfile.AttributeMapper;
import java.lang.classfile.AttributeMapper.AttributeStability;
import java.lang.classfile.Attributes;
import java.lang.classfile.ClassFile;
import java.lang.classfile.FieldElement;
import java.lang.classfile.constantpool.ConstantValueEntry;
import java.lang.constant.ConstantDesc;

import jdk.internal.classfile.impl.BoundAttribute;
import jdk.internal.classfile.impl.TemporaryConstantPool;
import jdk.internal.classfile.impl.UnboundAttribute;

/**
 * Models the {@link Attributes#constantValue() ConstantValue} attribute (JVMS
 * {@jvms 4.7.2}), which indicates this field's value is a constant and that
 * constant value.
 * <p>
 * This attribute only appears on fields, and does not permit {@linkplain
 * AttributeMapper#allowMultiple multiple instances} in a field.  It has a
 * data dependency on the {@linkplain AttributeStability#CP_REFS constant pool}.
 * <p>
 * This attribute was introduced in the Java Platform version 1.0.2, major
 * version {@value ClassFile#JAVA_1_VERSION}.
 *
 * @see Attributes#constantValue()
 * @jvms 4.7.2 The {@code ConstantValue} Attribute
 * @since 24
 */
public sealed interface ConstantValueAttribute
        extends Attribute<ConstantValueAttribute>, FieldElement
        permits BoundAttribute.BoundConstantValueAttribute,
                UnboundAttribute.UnboundConstantValueAttribute {

    /**
     * {@return the constant value of the field}
     */
    ConstantValueEntry constant();

    /**
     * {@return a {@code ConstantValue} attribute}
     * @param value the constant value
     */
    static ConstantValueAttribute of(ConstantValueEntry value) {
        return new UnboundAttribute.UnboundConstantValueAttribute(value);
    }

    /**
     * {@return a {@code ConstantValue} attribute}
     * @param value the constant value
     */
    static ConstantValueAttribute of(ConstantDesc value) {
        return of(switch(value) {
            case Integer i -> TemporaryConstantPool.INSTANCE.intEntry(i);
            case Float f -> TemporaryConstantPool.INSTANCE.floatEntry(f);
            case Long l -> TemporaryConstantPool.INSTANCE.longEntry(l);
            case Double d -> TemporaryConstantPool.INSTANCE.doubleEntry(d);
            case String s -> TemporaryConstantPool.INSTANCE.stringEntry(s);
            default -> throw new IllegalArgumentException("Invalid ConstantValueAttribute value: " + value);
        });
    }
}