How can I remove a substring from a given String?
You could easily use String.replace():
String helloWorld = "Hello World!";
String hellWrld = helloWorld.replace("o","");
You can use StringBuffer
StringBuffer text = new StringBuffer("Hello World");
text.replace( StartIndex ,EndIndex ,String);
replace('regex', 'replacement');
replaceAll('regex', 'replacement');
In your example,
String hi = "Hello World!"
String no_o = hi.replaceAll("o", "");