[DOCFIX] Fix links to java file examples in Java-API.md

relative links within the codebase do not render to usable links when
publishing to our documentation website.
`[description](/path/to/file)` will render as
`https://docs.alluxio.io/path/to/file`

replace with the full github url to the corresponding file in master
branch instead

pr-link: Alluxio#16834
change-id: cid-6ad346b38e0e2ff0c8018105930fae64261cd58b

docs/en/api/Java-API.md

@@ -337,6 +337,6 @@ org.apache.orc.Reader orc = org.apache.orc.OrcFile.createReader(
 ### Examples in Source Code
 
 There are several example Java programs. They are:
-* [`Alluxio native API`](/examples/src/main/java/alluxio/examples/AlluxioFS.java) 
-* [`Alluxio Hadoop-Compatible File System`](/examples/src/main/java/alluxio/examples/AlluxioHDFS.java)
-* [`HDFS`](/examples/src/main/java/alluxio/examples/HDFS.java)
+* [`Alluxio native API`](https://github.com/Alluxio/alluxio/tree/master/examples/src/main/java/alluxio/examples/AlluxioFS.java)
+* [`Alluxio Hadoop-Compatible File System`](https://github.com/Alluxio/alluxio/tree/master/examples/src/main/java/alluxio/examples/AlluxioHDFS.java)
+* [`HDFS`](https://github.com/Alluxio/alluxio/tree/master/examples/src/main/java/alluxio/examples/HDFS.java)