- 查看默认选项
$ java -XX:+PrintCommandLineFlags -version
-XX:ConcGCThreads=3 -XX:G1ConcRefinementThreads=10 -XX:GCDrainStackTargetSize=64 -XX:InitialHeapSize=525168320 -XX:MarkStackSize=4194304 -XX:MaxHeapSize=8402693120 -XX:MinHeapSize=6815736 -XX:+PrintCommandLineFlags -XX:ReservedCodeCacheSize=251658240 -XX:+SegmentedCodeCache -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseG1GC
openjdk version "17.0.5" 2022-10-18
OpenJDK Runtime Environment (build 17.0.5+8-Ubuntu-2ubuntu122.04)
OpenJDK 64-Bit Server VM (build 17.0.5+8-Ubuntu-2ubuntu122.04, mixed mode, sharing)java io
java 的io分字节流 ： 字节流都是 inputStream/outPutStream 字符流： reader/writer
方向：
| 类名 | 方法：读、写 | 字节、字符 |
|---|---|---|
| inputStream | read | byte |
| outputStream | write | byte |
| reader | read | char |
| writer | write | char |