java資料型別轉換，parseXXX(String)或valueOf(String)有什麼差別？

Question

基本型別的包裝類別的parseparseXXX(String)和valueOf(String)有什麼差別呀？

淡淡烟草味 · Answer

JDK8源碼

 /**
 * Returns an {@code Integer} object holding the value
 * extracted from the specified {@code String} when parsed
 * with the radix given by the second argument. The first argument
 * is interpreted as representing a signed integer in the radix
 * specified by the second argument, exactly as if the arguments
 * were given to the {@link #parseInt(java.lang.String, int)}
 * method. The result is an {@code Integer} object that
 * represents the integer value specified by the string.
 *
 * In other words, this method returns an {@code Integer}
 * object equal to the value of:
 *
 * 

 *  {@code new Integer(Integer.parseInt(s, radix))}
 * 
 *
 * @param      s   the string to be parsed.
 * @param      radix the radix to be used in interpreting {@code s}
 * @return     an {@code Integer} object holding the value
 *             represented by the string argument in the specified
 *             radix.
 * @exception NumberFormatException if the {@code String}
 *            does not contain a parsable {@code int}.
 */
public static Integer valueOf(String s, int radix) throws NumberFormatException {
    return Integer.valueOf(parseInt(s,radix));
}

這裡用Inteager來說明， valueOf 實際上呼叫了 parseInt。
parseInt方法是類別Integer的靜態方法，它的作用就是將字串轉換為整數int
valueOf也是Integer類別的靜態方法，它的作用是將字串轉換為Integer物件