blocks|key|976630|text|您可以尝试System.arraycopy或使用Arrays类中的数组函数，如java.util.Arrays.copyOf。这两者都应该在幕后给你带来原生的性能。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|976631|Arrays.copyOf可能对可读性有利，但它只是在Java1.6中引入的。|976632|+byte[]+src+=+{1,+2,+3,+4};
+byte[]+dst+=+Arrays.copyOf(src,+src.length);
+System.out.println(Arrays.toString(dst));|code-block|syntax|javascript|976633|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/javase/6/docs/api/java/lang/System.html#arraycopy%2528java.lang.Object,%2520int,%2520java.lang.Object,%2520int,%2520int%2529|1|http://java.sun.com/javase/6/docs/api/java/util/Arrays.html^0|5|G|O|6|13|N|5|G|0|O|6|1|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]|$9|16|A|17|1|18]]|E|$]]|$1|F|3|G|5|6|7|19|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1A|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]]]

You might try <a href="http://java.sun.com/javase/6/docs/api/java/lang/System.html#arraycopy%28java.lang.Object,%20int,%20java.lang.Object,%20int,%20int%29" rel="noreferrer"><code>System.arraycopy</code></a> or make use of array functions in the <a href="http://java.sun.com/javase/6/docs/api/java/util/Arrays.html" rel="noreferrer"><code>Arrays</code></a> class like <code>java.util.Arrays.copyOf</code>. Both should give you native performance under the hood.

Arrays.copyOf is probably favourable for readability, but was only introduced in java 1.6.

<pre><code> byte[] src = {1, 2, 3, 4};
 byte[] dst = Arrays.copyOf(src, src.length);
 System.out.println(Arrays.toString(dst));
</code></pre>

blocks|key|1190871|text|您可以使用System.arraycopy|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1190872|entityMap|0|LINK|mutability|MUTABLE|url|http://download.oracle.com/docs/cd/E17476_01/javase/1.4.2/docs/api/java/lang/System.html#arraycopy^0|5|G|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You can use <a href="http://download.oracle.com/docs/cd/E17476_01/javase/1.4.2/docs/api/java/lang/System.html#arraycopy" rel="nofollow noreferrer">System.arraycopy</a>

blocks|key|976683|text|您可以使用System.arrayCopy。它将元素从源数组复制到目标数组。Sun实现使用手工优化的汇编程序，因此速度很快。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|976684|entityMap|0|LINK|mutability|MUTABLE|url|http://download.oracle.com/docs/cd/E17409_01/javase/6/docs/api/java/lang/System.html#arraycopy(java.lang.Object,%2520int,%2520java.lang.Object,%2520int,%2520int))^0|5|G|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You can use <a href="http://download.oracle.com/docs/cd/E17409_01/javase/6/docs/api/java/lang/System.html#arraycopy(java.lang.Object,%20int,%20java.lang.Object,%20int,%20int)" rel="noreferrer">System.arrayCopy</a>. It copies elements from a source array to a destination array. The Sun implementation uses hand-optimized assembler, so this is fast.

blocks|key|976733|text|使用System.arraycopy()|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|976734|System.arraycopy(sourceArray,+
+++++++++++++++++sourceStartIndex,
+++++++++++++++++targetArray,
+++++++++++++++++targetStartIndex,
+++++++++++++++++length);|code-block|syntax|javascript|976735|例如，|976736|String[]+source+=+{+"alpha",+"beta",+"gamma"+};
String[]+target+=+new+String[source.length];
System.arraycopy(source,+0,+target,+0,+source.length);|976737|或者使用Arrays.copyOf()|976738|976739|target+=+Arrays.copyOf(source,+length);|976740|java.util.Arrays.copyOf(byte[]+source,+int+length)是在JDK1.6中添加的。|style|CODE|976741|copyOf()方法使用System.arrayCopy()复制数组，但比clone()更灵活，因为您可以复制数组的各个部分。|976742|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/6/docs/api/java/lang/System.html#arraycopy%2528java.lang.Object,%2520int,%2520java.lang.Object,%2520int,%2520int%2529|1|http://docs.oracle.com/javase/6/docs/api/java/util/Arrays.html#copyOf%2528byte%255B%255D,%2520int%2529^0|2|I|0|0|0|0|0|4|F|1|0|0|0|0|1E|0|0|8|C|I|11|7|0^^$0|@$1|2|3|4|5|6|7|17|8|@]|9|@$A|18|B|19|1|1A]]|C|$]]|$1|D|3|E|5|F|7|1B|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|1C|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|1D|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|1E|8|@]|9|@$A|1F|B|1G|1|1H]]|C|$]]|$1|O|3|J|5|6|7|1I|8|@]|9|@]|C|$]]|$1|P|3|Q|5|F|7|1J|8|@]|9|@]|C|$G|H]]|$1|R|3|S|5|6|7|1K|8|@$A|1L|B|1M|T|U]]|9|@]|C|$]]|$1|V|3|W|5|6|7|1N|8|@$A|1O|B|1P|T|U]|$A|1Q|B|1R|T|U]|$A|1S|B|1T|T|U]]|9|@]|C|$]]|$1|X|3|-4|5|6|7|1U|8|@]|9|@]|C|$]]]|Y|$Z|$5|10|11|12|C|$13|14]]|15|$5|10|11|12|C|$13|16]]]]

Use <a href="http://docs.oracle.com/javase/6/docs/api/java/lang/System.html#arraycopy%28java.lang.Object,%20int,%20java.lang.Object,%20int,%20int%29" rel="noreferrer">System.arraycopy()</a>

<pre><code>System.arraycopy(sourceArray, 
 sourceStartIndex,
 targetArray,
 targetStartIndex,
 length);
</code></pre>

Example,

<pre><code>String[] source = { "alpha", "beta", "gamma" };
String[] target = new String[source.length];
System.arraycopy(source, 0, target, 0, source.length);
</code></pre>

 
or use <a href="http://docs.oracle.com/javase/6/docs/api/java/util/Arrays.html#copyOf%28byte%5B%5D,%20int%29" rel="noreferrer">Arrays.copyOf()</a>
 Example,

<pre><code>target = Arrays.copyOf(source, length);
</code></pre>

<code>java.util.Arrays.copyOf(byte[] source, int length)</code> was added in JDK 1.6. 
 The <code>copyOf()</code> method uses <code>System.arrayCopy()</code> to make a copy of the array, but is more flexible than <code>clone()</code> since you can make copies of parts of an array.

blocks|key|976807|text|Java实际上有类似于memcpy()的东西。Unsafe类有一个与memcpy()基本相同的copyMemory()方法。当然，像memcpy()一样，它不提供内存覆盖、数据破坏等保护。目前还不清楚它到底是memcpy()还是memmove()。它可用于从实际地址复制到实际地址，或从引用复制到引用。请注意，如果使用引用，则必须提供偏移量(否则JVM将尽快终止)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|976808|Unsafe.copyMemory()可以工作(在我的旧PC上，每秒最高可达2+GB+)。使用风险自负。注意，并不是所有的JVM实现都存在不安全的类。|976809|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Java actually does have something just like memcpy(). The Unsafe class has a copyMemory() method that is essentially identical to memcpy(). Of course, like memcpy(), it provides no protection from memory overlays, data destruction, etc. It is not clear if it is really a memcpy() or a memmove(). It can be used to copy from actual addresses to actual addresses or from references to references. Note that if references are used, you must provide an offset (or the JVM will die ASAP). 

Unsafe.copyMemory() works (up to 2 GB per second on my old tired PC). Use at your own risk. Note that the Unsafe class does not exist for all JVM implementations.

blocks|key|976860|text|使用byteBufferViewVarHandle或byteArrayViewVarHandle。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|976861|这将允许您将一个“long”数组直接复制到一个"doubles“数组中，类似于：|976862|public+long[]+toLongs(byte[]+buf)+{
++++int+end+=+buf.length+>>+3;
++++long[]+newArray+=+new+long[end];
++++for+(int+ii+=+0;+ii+<+end;+%2B%2Bii)+{
++++++++newArray[ii]+=+(long)AS_LONGS_VH.get(buf,+ALIGN_OFFSET+%2B+ii+<<+3);
++++}
}

private+static+final+ALIGN_OFFSET+=+ByteBuffer.wrap(new+byte[0]).alignmentOffset(8);+
private+static+final+VarHandle+AS_LONGS_VH+=+MethodHandles.byteArrayViewVarHandle(long[].class,+ByteOrder.nativeOrder());|code-block|syntax|javascript|976863|这将让你像这样做一些黑客工作：|976864|float+thefloat+=+0.4;
int+floatBits;
_Static_assert(sizeof+theFloat+==+sizeof+floatBits,+"this+bit+twiddling+hack+requires+floats+to+be+equal+in+size+to+ints");
memcpy(&floatBits,+&thefloat,+sizeof+floatBits);|976865|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/invoke/MethodHandles.html#byteBufferViewVarHandle(java.lang.Class,java.nio.ByteOrder)^0|2|N|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|11|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|C|$]]|$1|M|3|N|5|H|7|13|8|@]|9|@]|C|$I|J]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]]]

Use <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/invoke/MethodHandles.html#byteBufferViewVarHandle(java.lang.Class,java.nio.ByteOrder)" rel="nofollow noreferrer">byteBufferViewVarHandle</a> or byteArrayViewVarHandle.

This will let you copy an array of "longs" directly to an array of "doubles" and similar with something like:

<pre><code>public long[] toLongs(byte[] buf) {
 int end = buf.length &gt;&gt; 3;
 long[] newArray = new long[end];
 for (int ii = 0; ii &lt; end; ++ii) {
 newArray[ii] = (long)AS_LONGS_VH.get(buf, ALIGN_OFFSET + ii &lt;&lt; 3);
 }
}

private static final ALIGN_OFFSET = ByteBuffer.wrap(new byte[0]).alignmentOffset(8); 
private static final VarHandle AS_LONGS_VH = MethodHandles.byteArrayViewVarHandle(long[].class, ByteOrder.nativeOrder());
</code></pre>

This will let you do the bit hacking like:

<pre><code>float thefloat = 0.4;
int floatBits;
_Static_assert(sizeof theFloat == sizeof floatBits, "this bit twiddling hack requires floats to be equal in size to ints");
memcpy(&amp;floatBits, &amp;thefloat, sizeof floatBits);
</code></pre>

blocks|key|977040|text|当您使用JDK+1.5%2B时，您应该使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|977041|System.arraycopy()|code-block|syntax|javascript|977042|而不是|977043|Arrays.copyOfRange()|977044|Beacuse+Arrays.copyOfRange()直到JDK1.6才被添加，因此您可能会得到|977045|Java+-+“Cannot+Find+Symbol”+error|977046|在该版本的JDK中调用Arrays.copyOfRange时。|977047|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

When you are using JDK 1.5+ You should use
<pre><code>System.arraycopy()
</code></pre>
Instead of
<pre><code>Arrays.copyOfRange()
</code></pre>
Beacuse Arrays.copyOfRange() wasn't added until JDK 1.6.So you might get
<pre><code>Java - “Cannot Find Symbol” error
</code></pre>
when calling Arrays.copyOfRange in that version of JDK.

I have a byte[] and would like to copy it into another byte[]. Maybe I am showing my simple 'C' background here, but is there an equivalent to memcpy() on byte arrays in Java?

Is there an equivalent to memcpy() in Java?

Java

我有一个byte[]，想把它复制到另一个byte[]中。也许我在这里展示了我的简单的“C”背景，但是在Java中有没有与字节数组上的memcpy()等价的方法呢？

问在Java中有没有等同于memcpy()的东西？
EN

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