补充(equals比较)

Object中的equals比较的是地址

  public boolean equals(Object obj) {
    return (this == obj);
}

java.lang.String类中equals的方法

equals判断相等依据

策略：如果与目标相等返回0，小于目标返回值小于0，大于目标返回值大于0

@Native static final byte LATIN1 = 0;
@Native static final byte UTF16  = 1;

  /**
 * Compares this string to the specified object.  The result is {@code
 * true} if and only if the argument is not {@code null} and is a {@code
 * String} object that represents the same sequence of characters as this
 * object.
 *
 * <p>For finer-grained String comparison, refer to
 * {@link java.text.Collator}.
 *
 * @param  anObject
 *         The object to compare this {@code String} against
 *
 * @return  {@code true} if the given object represents a {@code String}
 *          equivalent to this string, {@code false} otherwise
 *
 * @see  #compareTo(String)
 * @see  #equalsIgnoreCase(String)
 */
public boolean equals(Object anObject) {
    if (this == anObject) {
        return true;
    }
    if (anObject instanceof String) {
        String aString = (String)anObject;
        if (coder() == aString.coder()) {
            return isLatin1() ? StringLatin1.equals(value, aString.value)
                              : StringUTF16.equals(value, aString.value);
        }
    }
    return false;
}

private boolean isLatin1() {
     return COMPACT_STRINGS && coder == LATIN1;
}

###StringLatin1.equals|
@HotSpotIntrinsicCandidate
    public static boolean equals(byte[] value, byte[] other) {
        if (value.length == other.length) {
            for (int i = 0; i < value.length; i++) {
                if (value[i] != other[i]) {
                    return false;
                }
            }
            return true;
        }
        return false;
    }

###StringUTF16.equals|
@HotSpotIntrinsicCandidate
    public static boolean equals(byte[] value, byte[] other) {
        if (value.length == other.length) {
            int len = value.length >> 1;
            for (int i = 0; i < len; i++) {
                if (getChar(value, i) != getChar(other, i)) {
                    return false;
                }
            }
            return true;
        }
        return false;
    }

注：更细粒度的equals比较，先比较地址是否相同，看其是否为空，最后看其编码值比较