ByteOrder.java

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package java.nio;

import jdk.internal.misc.Unsafe;

/**
 * A typesafe enumeration for byte orders.
 *
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @since 1.4
 */
// 查看底层的字节存储顺序是大端还是小端
public final class ByteOrder {
    private String name;
    
    /**
     * Constant denoting big-endian byte order.
     * In this order, the bytes of a multibyte value are ordered from most significant to least significant.
     */
    public static final ByteOrder BIG_ENDIAN = new ByteOrder("BIG_ENDIAN");
    /**
     * Constant denoting little-endian byte order.
     * In this order, the bytes of a multibyte value are ordered from least significant to most significant.
     */
    public static final ByteOrder LITTLE_ENDIAN = new ByteOrder("LITTLE_ENDIAN");
    
    // Retrieve the native byte order. It's used early during bootstrap, and must be initialized after BIG_ENDIAN and LITTLE_ENDIAN.
    private static final ByteOrder NATIVE_ORDER = Unsafe.getUnsafe().isBigEndian() ? ByteOrder.BIG_ENDIAN : ByteOrder.LITTLE_ENDIAN;
    
    private ByteOrder(String name) {
        this.name = name;
    }
    
    /**
     * Retrieves the native byte order of the underlying platform.
     *
     * <p> This method is defined so that performance-sensitive Java code can
     * allocate direct buffers with the same byte order as the hardware.
     * Native code libraries are often more efficient when such buffers are
     * used.  </p>
     *
     * @return The native byte order of the hardware upon which this Java
     * virtual machine is running
     */
    // 返回当前系统下底层字节的顺序
    public static ByteOrder nativeOrder() {
        return NATIVE_ORDER;
    }
    
    /**
     * Constructs a string describing this object.
     *
     * <p> This method returns the string {@code "BIG_ENDIAN"} for {@link #BIG_ENDIAN} and {@code "LITTLE_ENDIAN"} for {@link #LITTLE_ENDIAN}.
     *
     * @return The specified string
     */
    // 返回描述此对象的字符串"BIG_ENDIAN"或"LITTLE_ENDIAN"
    public String toString() {
        return name;
    }
}