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Learn Java: Manipulating Variables

Let’s say we are writing a program that represents a user’s bank account. With variables, we know how to store a balance! We’d use a double, the primitive type that can hold big decimal numbers. But how would we deposit and withdraw from the account?

Lucky for us, we have the ability to manipulate the value of our variables. We can use expressions, arithmetic operators, and more in order to change our variables’ values.

For example, Java has built-in arithmetic operations that perform calculations on numeric values:

// declare initial balance double balance = 20000.99; // declare deposit amount double depositAmount = 1000.00; // store result of calculation in our original variable balance = balance + depositAmount;

In the final line of the code above, we used the expression balance + depositAmount to determine the new value of the balance variable. When an expression is executed, it produces a single value.

The data type of a variable plays a large role in the operations we can use to manipulate it. We can think of a data type as a combination of a set of values, and a set of operations on those values. For example, the double data type is comprised of values like 4.8 and operations like addition (+). For now, we’ll mainly focus on the set of operations that can be used on numbers and booleans.

The data type of an expression is determined by the resulting value. For example, an expression that uses two int values will evaluate to an int value. If an expression contains a double value, then the resulting value will also be type double.

Throughout this lesson, we will learn how to manipulate variables of different data types.



In the file, we have defined two integers mystery1 and mystery2.

We will talk about these operators, among others, in the rest of the lesson.

Use System.out.println() to print the variable that holds a value of 2.

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