There are times when we want to treat a value of a primitive type as an object. Java provides a wrapper class for each primitive data type. Each wrapper class encapsulates its corresponding primitive data type. It is said to “wrap” a value of that type.
Section 1 - The Integer Class
The Integer class wraps an int value. You can create an Integer object by assignment to an int literal, variable, or expression.
Integer i = 5; // Assignment to an int literal
Integer j = 2+7; // Assignment to an int expression
int x = 4;
Integer k = x; // Assignment to an int variable
System.out.println(i); // Prints 5
System.out.println(j); // Prints 9
System.out.println(k); // Prints 4
Section 1a - The parseInt Method
The static parseInt method converts a string formatted as a signed integer to an int value.
String s = “100”; // s contains string “100”
int z = Integer.parseInt(s); // z contains int value 100
int y = Integer.parseInt(“-200”); // y contains int value 200
The parseInt method can be called with a second argument that indicates the numeric base of the string.
System.out.println(Integer.parseInt("8000",16)); // Prints 32768
System.out.println(Integer.parseInt("-8000",16)); // Prints -32768
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