how to delete default values in text field using selenium?

For page object model -

 @FindBy(xpath="//foo")
   public WebElement textBox;

now in your function

 public void clearExistingText(String newText){
    textBox.clear();
    textBox.sendKeys(newText);
  }

for general selenium architecture -

driver.findElement(By.xpath("//yourxpath")).clear();
driver.findElement(By.xpath("//yourxpath")).sendKeys("newText");

And was the code helpful? Because the code you are writing should do the thing:

driver.findElement("locator").clear();

If it does not help, then try this:

WebElement toClear = driver.findElement("locator");
toClear.sendKeys(Keys.CONTROL + "a");
toClear.sendKeys(Keys.DELETE);

maybe you will have to do some convert of the Keys.CONTROL + "a" to CharSequence, but the first approach should do the magic