Answers for "why a string belong to a class"

string method example in java

public char charAt(int index)
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String x = "airplane";
System.out.println( x.charAt(2) ); // output is 'r'

string method example in java

public String concat(String s)

String x = "book";
System.out.println( x.concat(" author") ); // output is "book author"