Use app:counterEnabled="true"

• Whether the character counter functionality is enabled or not in this layout.

Also use app:counterMaxLength="250"

• Sets the max length to display at the character counter.

Try this

<android.support.design.widget.TextInputLayout
    android:id="@+id/post_text_input_base"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:counterEnabled="true"
    app:counterMaxLength="250">

    <EditText
        android:id="@+id/post_text_input"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="UserName" />
</android.support.design.widget.TextInputLayout>

OUTPUT

EDIT

public class RecyclerViewActivity extends AppCompatActivity {

    TextInputLayout postTextInputBase;
    EditText postTextInputEditText;

    int textLength = 9;
    int len = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_recycler_view);

        postTextInputBase = findViewById(R.id.post_text_input_base);

        postTextInputEditText = findViewById(R.id.post_text_input);

        postTextInputBase.setHint(textLength + " characters left");

        postTextInputEditText.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {

                // first check your EditText is empty or not
                if (!TextUtils.isEmpty(postTextInputEditText.getText().toString())) {

                    int len = postTextInputEditText.getText().toString().length();
                    // than check that editText text length is less than max length or not
                    // for test case i have set max length 10
                    if (len < 9) {
                        // if length of text is less than max length than use minus one from max length and set error in your text input layout
                        textLength--;
                    } else {
                        textLength++;
                        
                    }
                    
                    postTextInputBase.setHint(textLength + " characters left");
                } else {
                    textLength = 9;
                }
            }

            @Override
            public void afterTextChanged(Editable s) {

              if(postTextInputEditText.getText().toString().isEmpty()){
                  textLength = 9;
                  postTextInputBase.setHint(textLength + " characters left");
              }
            }
        });


    }


}

OUTPUT

EDIT 2 If you need set hint than use this

postTextInputBase.setHint(textLength + " characters left");

OUTPUT

NOTE Don't forgot to set android:maxLength="10" in edittext

Try this. Works with your existing code.

int charactersLeft = 256;
final TextInputLayout postTextInputBase = findViewById(R.id.post_text_input_base);
final TextInputEditText postTextInput = findViewById(R.id.post_text_input);

postTextInput.addTextChangedListener(new TextWatcher() {

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {           
        }

        @Override
        public void afterTextChanged(Editable s) {
           if (s.length() == 0) {
                postTextInputBase.setHint(null);
            }else {
                postTextInputBase.setHint((charactersLeft - s.length()) + " characters left");
            }
        }
    });

and Add android:maxLength="256" to your TextInputEditText

You may do it programatically using setOnKeyListener on the edit text.

TextInputLayout postTextInputBase = findViewById(R.id.post_text_input_base);
TextInputEditText postTextInput = findViewById(R.id.post_text_input);
postTextInput.setOnKeyListener((v, keyCode, event) -> {
        // Do other things needed
        postTextInputBase.setHint("Characters left: " + (256 - postTextInput.getText().length()));
        return false;
});

To change Hint text only you can just change it on focus change.

editText.setOnFocusChangeListener(new View.OnFocusChangeListener() {
        @Override
        public void onFocusChange(View v, boolean hasFocus) {
            if(hasFocus)
                editText.setHint("Enter name");
            else
                editText.setHint("Name");
        }
    });