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Share char array buffers in java.lang.String #191

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Merged
dlunch merged 4 commits into from
Jul 25, 2026
Merged

Share char array buffers in java.lang.String #191

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9a6b936
Share char array buffers in java.lang.String
dlunch Jul 25, 2026
f8745d5
Match the JDK on regionMatches and drop leftover io copies
dlunch Jul 25, 2026
e974800
Reject a corrupt String range instead of panicking
dlunch Jul 25, 2026
13cc16f
Name the sharing constructor after its char array
dlunch Jul 25, 2026
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14 changes: 3 additions & 11 deletions java_runtime/src/classes/java/io/buffered_reader.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ use alloc::{vec, vec::Vec};

use java_class_proto::{JavaFieldProto, JavaMethodProto};
use java_constants::{ClassAccessFlags, FieldAccessFlags, MethodAccessFlags};
use jvm::{Array, ClassInstanceRef, JavaChar, Jvm, Result};
use jvm::{Array, ClassInstanceRef, JavaChar, Jvm, Result, runtime::JavaLangString};

use crate::{
RuntimeClassProto, RuntimeContext,
Expand Down Expand Up @@ -336,11 +336,7 @@ impl BufferedReader {
return Ok(None.into());
}

let line_length = line.len();
let mut chars = jvm.instantiate_array("C", line_length).await?;
jvm.store_array(&mut chars, 0, line).await?;
let value = jvm.new_class("java/lang/String", "([CII)V", (chars, 0, line_length as i32)).await?;
return Ok(value.into());
return Ok(JavaLangString::from_utf16(jvm, line).await?.into());
}
next_char = jvm.get_field(&this, "nextChar", "I").await?;
n_chars = jvm.get_field(&this, "nChars", "I").await?;
Expand All @@ -367,11 +363,7 @@ impl BufferedReader {
jvm.put_field(&mut this, "skipLF", "Z", true).await?;
}

let line_length = line.len();
let mut chars = jvm.instantiate_array("C", line_length).await?;
jvm.store_array(&mut chars, 0, line).await?;
let value = jvm.new_class("java/lang/String", "([CII)V", (chars, 0, line_length as i32)).await?;
return Ok(value.into());
return Ok(JavaLangString::from_utf16(jvm, line).await?.into());
}

line.extend(buffered);
Expand Down
8 changes: 3 additions & 5 deletions java_runtime/src/classes/java/io/data_input_stream.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@ use alloc::{vec, vec::Vec};

use java_class_proto::JavaMethodProto;
use java_constants::MethodAccessFlags;
use jvm::{Array, ClassInstanceRef, JavaChar, Jvm, Result};
use jvm::{Array, ClassInstanceRef, JavaChar, Jvm, Result, runtime::JavaLangString};

use crate::{
RuntimeClassProto, RuntimeContext,
Expand Down Expand Up @@ -156,7 +156,7 @@ impl DataInputStream {
tracing::debug!("java.io.DataInputStream::readUTF({this:?})");

let length: i32 = jvm.invoke_virtual(&this, "readUnsignedShort", "()I", ()).await?;
let mut java_array = jvm.instantiate_array("B", length as usize).await?;
let java_array = jvm.instantiate_array("B", length as usize).await?;
let _: () = jvm.invoke_virtual(&this, "readFully", "([BII)V", (java_array.clone(), 0, length)).await?;
let bytes: Vec<i8> = jvm.load_array(&java_array, 0, length as usize).await?;
let bytes: Vec<u8> = bytes.into_iter().map(|value| value as u8).collect();
Expand Down Expand Up @@ -192,9 +192,7 @@ impl DataInputStream {
}
}

java_array = jvm.instantiate_array("C", chars.len()).await?;
jvm.store_array(&mut java_array, 0, chars).await?;
Ok(jvm.new_class("java/lang/String", "([C)V", (java_array,)).await?.into())
Ok(JavaLangString::from_utf16(jvm, chars).await?.into())
}

async fn read_utf_from_input(jvm: &Jvm, _: &mut RuntimeContext, input: ClassInstanceRef<DataInput>) -> Result<ClassInstanceRef<String>> {
Expand Down
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