Conversion of any type to String use,

    a. String.valueOf( )
    b. toString( )

Conversion of String to any type use,

   a. any_type.parse() 

Converting any type to String:

public class Conversion {
public static void main(String[] args) {
int a=10;
double b=5.5;
//Converting other types to String
String s1=String.valueOf(a);
String s2=String.valueOf(b);
//concatination of two strings
String s3=s1+s2;
System.out.println(s3);
}
}

Output:

105.5 

Converting String to any type:

public class Conversion {
public static void main(String[] args) {
String s1="10";
String s2="11.5";
//converting String to Integer
int a=Integer.parseInt(s1);
//converting String to Double
double b=Double.parseDouble(s2);
double res=(double)a+b;
System.out.println("Result= "+res);
}
}

Output

Result= 21.5