What does “double” mean in Java?

In Java, `double` is a data type used to represent double-precision floating point numbers. It can store decimal values within a larger range and offers higher precision.

The `double` type uses 64 bits to store data, with 1 bit for the sign, 11 bits for the exponent, and the remaining 52 bits for the mantissa. This allows it to represent very large or very small numbers with relatively high precision.

Here is an example demonstrating how to declare and use a variable of type `double`:

double num1 = 3.14159;  // 声明并初始化一个 double 类型的变量
double num2 = 2.71828;
double sum = num1 + num2;  // 对两个 double 类型的变量进行加法运算
System.out.println("Sum: " + sum);  // 打印输出结果

In the example above, we declare two variables, `num1` and `num2`, of type `double`, then add them together and store the result in a variable named `sum`. Finally, we display the result on the console by using a print statement.

It should be noted that due to the nature of floating-point numbers, rounding errors may occur when performing calculations with non-integer values. Therefore, when comparing two `double` values, it is advisable to avoid using the exact equality operator (e.g. `==`) and instead use an approximate equality comparison operator (e.g. using `Math.abs()` for comparison).