如何从Java中的另一个数组创建子数组？
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How to create a sub array from another array in Java?
提问by Gain
How to create a sub-array from another array? Is there a method that takes the indexes from the first array such as:
如何从另一个数组创建子数组？是否有一种方法可以从第一个数组中获取索引，例如：
methodName(object array, int start, int end)
I don't want to go over making loops and making my program suffer.
我不想重复制作循环并使我的程序受到影响。
I keep getting error:
我不断收到错误：
cannot find symbol method copyOfRange(int[],int,int)
找不到符号方法 copyOfRange(int[],int,int)
This is my code:
这是我的代码：
import java.util.*;
public class testing
{
public static void main(String [] arg)
{
int[] src = new int[] {1, 2, 3, 4, 5};
int b1[] = Arrays.copyOfRange(src, 0, 2);
}
}
回答by Jigar Joshi
回答by Gerco Dries
Yes, it's called System.arraycopy(Object, int, Object, int, int).
是的，它被称为System.arraycopy(Object, int, Object, int, int)。
It's still going to perform a loop somewhere though, unless this can get optimized into something like REP STOSWby the JIT (in which case the loop is inside the CPU).
尽管如此，它仍然会在某处执行一个循环，除非它可以REP STOSW通过 JIT优化成类似的东西（在这种情况下，循环在 CPU 内部）。
int[] src = new int[] {1, 2, 3, 4, 5};
int[] dst = new int[3];
System.arraycopy(src, 1, dst, 0, 3); // Copies 2, 3, 4 into dst
回答by Bozho
Arrays.copyOfRange(..)was added in Java 1.6. So perhaps you don't have the latest version. If it's not possible to upgrade, look at System.arraycopy(..)
Arrays.copyOfRange(..)在 Java 1.6 中添加。所以也许你没有最新版本。如果无法升级，请查看System.arraycopy(..)
回答by AlexR
I you are using java prior to version 1.6 use System.arraycopy()instead. Or upgrade your environment.
我使用 1.6 版之前的 javaSystem.arraycopy()代替。或者升级你的环境。
回答by Milan Jaros
int newArrayLength = 30;
int[] newArray = new int[newArrayLength];
System.arrayCopy(oldArray, 0, newArray, 0, newArray.length);
回答by Merky
The code is correct so I'm guessing that you are using an older JDK. The javadoc for that method says it has been there since 1.6. At the command line type:
代码是正确的，所以我猜你使用的是旧版 JDK。该方法的 javadoc 说它从 1.6 开始就存在了。在命令行输入：
java -version
I'm guessing that you are not running 1.6
我猜你没有运行 1.6
回答by Alessandro Muzzi
Using Apache ArrayUtilsdownloadable at this linkyou can easy use the method
使用可在此链接下载的Apache ArrayUtils，您可以轻松使用该方法
subarray(boolean[] array, int startIndexInclusive, int endIndexExclusive)
"boolean" is only an example, there are methods for all primitives java types
“boolean”只是一个例子，所有原语java类型都有方法
回答by Dhirendra Pratap
Use copyOfRange method from java.util.Arrays class:
使用 java.util.Arrays 类中的 copyOfRange 方法：
int[] newArray = Arrays.copyOfRange(oldArray, startIndex, endIndex);
int[] newArray = Arrays.copyOfRange(oldArray, startIndex, endIndex);
For more details:
更多细节：
回答by enator
JDK >= 1.8
JDK >= 1.8
I agree with all the answers above. There is also a nice way with Java 8 Streams:
我同意上面的所有答案。Java 8 Streams 还有一个很好的方法：
int[] subArr = IntStream.range(startInclusive, endExclusive)
.map(i -> src[i])
.toArray();
The benefit about this is, it can be useful for many different types of "src" array and helps to improve writing pipeline operations on the stream.
这样做的好处是，它可以用于许多不同类型的“src”数组，并有助于改进流上的写入管道操作。
Not particular about this question, but for example, if the source array was double[]and we wanted to take average()of the sub-array:
不是特别关注这个问题，但例如，如果源数组是double[]并且我们想要取average()子数组：
double avg = IntStream.range(startInclusive, endExclusive)
.mapToDouble(index -> src[index])
.average()
.getAsDouble();
