how to remove letter or digits from a string java code example

Example 1: how to remove all special characters from a string in java

String str= "This#string%contains^special*characters&.";   
str = str.replaceAll("[^a-zA-Z0-9]", " ");  
System.out.println(str);

Example 2: how to delete character in string java

# subString(int start, int end);

String a = "Hello!";
b = a.subString(0,a.length()-1) #Remove the last String
# b should be "Hello" then