how to delete characters from string code example

Example 1: java string remove character

String str = "abcdDCBA123";
String strNew = str.replace("a", ""); // strNew is 'bcdDCBA123'

Example 2: how to remove letters from string

public extractLetters(String str){
	String result="";
	for(int i= 0; i< str.length; i++){
	    if(Character.isLetter(str.charAt(i))){
	    result+=str.charAt(i);
	  	}
	}

Example 3: remove charachter from string

if(String.charAt(1) == String.charAt(2){
   //I want to remove the individual character at index 2. 
}