src/java.base/share/classes/java/lang/classfile/constantpool/LoadableConstantEntry.java

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package java.lang.classfile.constantpool;

import java.lang.classfile.CodeBuilder;
import java.lang.classfile.Opcode;
import java.lang.classfile.TypeKind;
import java.lang.classfile.instruction.ConstantInstruction;
import java.lang.constant.ConstantDesc;

/**
 * Marker interface for constant pool entries suitable for loading via the
 * {@link ConstantInstruction.LoadConstantInstruction ldc} instructions.
 * <p>
 * The use of a {@code LoadableConstantEntry} is modeled by a {@link ConstantDesc}.
 * Conversions are through {@link ConstantPoolBuilder#loadableConstantEntry(ConstantDesc)}
 * and {@link #constantValue()}.
 *
 * @see CodeBuilder#ldc(LoadableConstantEntry)
 * @jvms 4.4 The Constant Pool
 * @sealedGraph
 * @since 24
 */
public sealed interface LoadableConstantEntry extends PoolEntry
        permits ClassEntry, ConstantDynamicEntry, ConstantValueEntry, MethodHandleEntry, MethodTypeEntry {

    /**
     * {@return a symbolic descriptor of this constant}
     *
     * @see ConstantPoolBuilder#loadableConstantEntry(ConstantDesc)
     */
    ConstantDesc constantValue();

    /**
     * {@return the data type of this constant}
     * <p>
     * If the data type is of {@linkplain TypeKind#slotSize() category} 2, this
     * constant must be loaded with {@link Opcode#LDC2_W ldc2_w}; otherwise, the
     * data type is of category 1, and this constant must be loaded with {@link
     * Opcode#LDC ldc} or {@link Opcode#LDC_W ldc_w}.
     */
    default TypeKind typeKind() {
        return TypeKind.REFERENCE;
    }
}