[Java] String.valueOf vs toString

차이점 

String.valueOf 같은 경우 해당 값이 null 일때는 String 형 "null"반환

toString 같은 경우 NullPointException 발생

 

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왜?

String.valueOf 같은 경우에는 아래와 같이 해당 객체가 null 경우에 대한 조건문이 있지만,

toString은 존재하지 않는다.

String.valueOf 구현체

  /**
     * Returns the string representation of the {@code Object} argument.
     *
     * @param   obj   an {@code Object}.
     * @return  if the argument is {@code null}, then a string equal to
     *          {@code "null"}; otherwise, the value of
     *          {@code obj.toString()} is returned.
     * @see     java.lang.Object#toString()
     */
    public static String valueOf(Object obj) {
        return (obj == null) ? "null" : obj.toString();
    }

toString 구현체

   /**
     * Returns a {@code String} object representing this
     * {@code Integer}'s value. The value is converted to signed
     * decimal representation and returned as a string, exactly as if
     * the integer value were given as an argument to the {@link
     * java.lang.Integer#toString(int)} method.
     *
     * @return  a string representation of the value of this object in
     *          base 10.
     */
    public String toString() {
        return toString(value);
    }

 

 

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Example

public class Main {

	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub

		Map<String, Integer> testList = new HashMap<String, Integer>();

		testList.put("A", 100);

		// valueof = "null"
		String valueOf = String.valueOf(testList.get("B"));

		System.out.println(valueOf);

		try {
			// NPE 발생
			String toString = (testList.get("B")).toString();
			System.out.println(toString);
			
		} catch (NullPointerException e) {
			System.out.println("NPE 발생");
		}
	}
}