refactor: initialize all instance fields in constructors

Drop inline field initializers across the context and stream classes so
every instance field is assigned in the constructor. In the NativeObject
streams arena is assigned right after super() and before the try, so the
catch's close() -> tryClose() -> arena.close() cleanup still holds.

Convention only; no checkstyle rule enforces it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: dfa1

zstd/src/main/java/io/github/dfa1/zstd/ZstdCompressCtx.java

@@ -19,11 +19,12 @@
 /// }
 public final class ZstdCompressCtx extends NativeObject {
 
-    private int level = Zstd.defaultCompressionLevel();
+    private int level;
 
     /// Creates a new compression context at the default level.
     public ZstdCompressCtx() {
         super(create());
+        this.level = Zstd.defaultCompressionLevel();
     }
 
     private static MemorySegment create() {

zstd/src/main/java/io/github/dfa1/zstd/ZstdCompressStream.java

@@ -30,9 +30,9 @@
 /// Not thread-safe: confine an instance to a single thread.
 public final class ZstdCompressStream extends NativeObject {
 
-    private final Arena arena = Arena.ofConfined();
-    private final ZstdStreamBuffer in = new ZstdStreamBuffer(arena);
-    private final ZstdStreamBuffer out = new ZstdStreamBuffer(arena);
+    private final Arena arena;
+    private final ZstdStreamBuffer in;
+    private final ZstdStreamBuffer out;
 
     /// Creates a streaming compressor at the default level.
     public ZstdCompressStream() {
@@ -54,6 +54,9 @@ public ZstdCompressStream(int level, ZstdDictionary dictionary) {
         // Own the context first, so any failure setting it up is cleaned up by
         // close() — one release path, no leak on a half-built stream.
         super(createCctx());
+        this.arena = Arena.ofConfined();
+        this.in = new ZstdStreamBuffer(arena);
+        this.out = new ZstdStreamBuffer(arena);
         try {
             NativeCall.checkReturnValue(() -> (long) Bindings.CCTX_SET_PARAMETER.invokeExact(
                     ptr(), ZstdCompressParameter.COMPRESSION_LEVEL.value(), level));

zstd/src/main/java/io/github/dfa1/zstd/ZstdDecompressStream.java

@@ -14,9 +14,9 @@
 /// Not thread-safe: confine an instance to a single thread.
 public final class ZstdDecompressStream extends NativeObject {
 
-    private final Arena arena = Arena.ofConfined();
-    private final ZstdStreamBuffer in = new ZstdStreamBuffer(arena);
-    private final ZstdStreamBuffer out = new ZstdStreamBuffer(arena);
+    private final Arena arena;
+    private final ZstdStreamBuffer in;
+    private final ZstdStreamBuffer out;
 
     /// Creates a streaming decompressor.
     public ZstdDecompressStream() {
@@ -30,6 +30,9 @@ public ZstdDecompressStream(ZstdDictionary dictionary) {
         // Own the context first, so any failure setting it up is cleaned up by
         // close() — one release path, no leak on a half-built stream.
         super(createDctx());
+        this.arena = Arena.ofConfined();
+        this.in = new ZstdStreamBuffer(arena);
+        this.out = new ZstdStreamBuffer(arena);
         try {
             if (dictionary != null) {
                 loadDictionary(dictionary);

zstd/src/main/java/io/github/dfa1/zstd/ZstdInputStream.java

@@ -28,16 +28,16 @@
 public final class ZstdInputStream extends InputStream {
 
     private final InputStream in;
-    private final Arena arena = Arena.ofConfined();
+    private final Arena arena;
     private final MemorySegment dctx;
     private final MemorySegment inSeg;
     private final MemorySegment outSeg;
     private final long outCap;
-    private final ZstdStreamBuffer inBuf = new ZstdStreamBuffer(arena);
-    private final ZstdStreamBuffer outBufView = new ZstdStreamBuffer(arena);
+    private final ZstdStreamBuffer inBuf;
+    private final ZstdStreamBuffer outBufView;
     private final byte[] feed;
     private final byte[] hold;
-    private final byte[] single = new byte[1];
+    private final byte[] single;
     private int holdStart;
     private int holdEnd;
     private boolean inputEof;
@@ -59,6 +59,10 @@ public ZstdInputStream(InputStream in) {
     /// @param dictionary the dictionary the frame was compressed against, or `null` for none
     public ZstdInputStream(InputStream in, ZstdDictionary dictionary) {
         this.in = Objects.requireNonNull(in, "in");
+        this.arena = Arena.ofConfined();
+        this.inBuf = new ZstdStreamBuffer(arena);
+        this.outBufView = new ZstdStreamBuffer(arena);
+        this.single = new byte[1];
         MemorySegment d = null;
         try {
             d = (MemorySegment) Bindings.CREATE_DCTX.invokeExact();

zstd/src/main/java/io/github/dfa1/zstd/ZstdOutputStream.java

@@ -35,16 +35,16 @@ public final class ZstdOutputStream extends OutputStream {
     private static final int ZSTD_E_END = 2;
 
     private final OutputStream out;
-    private final Arena arena = Arena.ofConfined();
+    private final Arena arena;
     private final MemorySegment cctx;
     private final MemorySegment inSeg;
     private final MemorySegment outSeg;
     private final long inCap;
     private final long outCap;
-    private final ZstdStreamBuffer in = new ZstdStreamBuffer(arena);
-    private final ZstdStreamBuffer outBuf = new ZstdStreamBuffer(arena);
+    private final ZstdStreamBuffer in;
+    private final ZstdStreamBuffer outBuf;
     private final byte[] drain;
-    private final byte[] single = new byte[1];
+    private final byte[] single;
     private boolean closed;
 
     /// Wraps `out`, compressing at the library default level.
@@ -96,6 +96,10 @@ private void setPledgedSrcSize(long pledgedSrcSize) {
     /// @param dictionary the dictionary to compress against, or `null` for none
     public ZstdOutputStream(OutputStream out, int level, ZstdDictionary dictionary) {
         this.out = Objects.requireNonNull(out, "out");
+        this.arena = Arena.ofConfined();
+        this.in = new ZstdStreamBuffer(arena);
+        this.outBuf = new ZstdStreamBuffer(arena);
+        this.single = new byte[1];
         MemorySegment c = null;
         try {
             c = (MemorySegment) Bindings.CREATE_CCTX.invokeExact();