Java is a very widely used language, whether it is in business, or in personal use. However, your computer may not have Java installed, there is no use of Java applications, Java is not a must on the computer components.
The most likely use of Java programs around your device is likely to be your smartphone - if it is installed on an Android operating system. A significant portion of the Android operating system is Java-based. In fact, if you are interested in Android development, Java is one of the technologies you need to learn.