The .dmg file is a disk image format native to . This particular package includes the essential tools for Java development:
This guide provides a basic overview of installing and setting up JDK 7u80 on macOS. Keep in mind that using older versions of Java may pose security risks, as they may not receive current security updates. jdk-7u80-macosx-x64.dmg
By default, it installs to /Library/Java/JavaVirtualMachines/jdk1.7.0_80.jdk/Contents/Home . Accessing the File jdk-7u80-macosx-x64.dmg