how to get Substring in android

In this blog explain how to get Substring from String in android..

String str  = "1234567890" ;
String Char  =  "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

for example...

Step first - get string legth
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//get length
int lenth=Char.length();

// you get last string
String Lastchar=Char.substring(Char.length()-1); //same as  str
Log.e("Lastchar...",Lastchar);
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Step 2- get Substring
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// you get last string 
String substr=Char.substring(0,3); //same as  str
Log.e("substring...",substr);

output:- substr - ABC;
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Step 2- How to remove space
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 String str = the good boy

// you get last string 
String substr=str.substring(0,4).trim(); //same as  str

Log.e("substring...",substr);

output:- substr- the;