Java Java.util.Arrays.copyOfRange()用法及代码示例

此方法在原始数组的指定范围内创建元素的副本。

用法:

public static int[] copyOfRange(int[] original_array, int from_index, int to_index)

original_array：要复制的数组
from_index：要复制范围的起始索引
to_index要复制范围的结束索引

使用此方法时要记住的重要事项：

初始索引(即(from_index)必须在0到original_array.length之内
最终索引，即(to_index)可以大于或等于原始数组的长度。如果它大于原始数组，则将0分配给索引大于或等于original.length-from的副本。
返回数组的长度为to-from
它是Arrays类的一种方法

异常

ArrayIndexOutOfBoundsException：如果初始索引即(from_index)
超出原始数组的范围
IllegalArgumentException：如果form_index> to_index抛出此错误
NullPointerException ：如果原始数组为null，则抛出此错误

变化：

copyOfRange(boolean[] original, int from, int to)
copyOfRange(byte[] original, int from, int to)
copyOfRange(char[] original, int from, int to)
copyOfRange(double[] original, int from, int to)
copyOfRange(float[] original, int from, int to)
copyOfRange(int[] original, int from, int to)
copyOfRange(long[] original, int from, int to)
copyOfRange(short[] original, int from, int to)
copyOfRange(T[] original, int from, int to)
copyOfRange(U[] original, int from, int to, Class newType)

让我们通过一个例子来理解这一点：

// Java program to illustrate  
// copyOfRange method 
import java.util.Arrays; 
class GFG { 
public static void main(String args[]) 
    { 
        int arr[] = { 12, 13, 14, 15, 16, 17, 18 }; 
  
        // to index is within the range 
        int[] copy = Arrays.copyOfRange(arr, 2, 6); 
        for (int i : copy) 
            System.out.print(i + "  "); 
  
        System.out.println(); 
        // to index is out of range 
        // It assigns Zero to all the index out of range 
        int[] copy1 = Arrays.copyOfRange(arr, 4, arr.length + 3); 
  
        for (int i : copy1) 
            System.out.print(i + "  "); 
  
        // It throws IIlegalArgumentException 
        // int[] copy2 = Arrays.copyOfRange(arr, 5, 3); 
  
        // It throws ArrayIndexOutOfBoundsException 
        // int[] copy2 = Arrays.copyOfRange(arr, 10, arr.length + 5); 
    } 
}

输出：

14  15  16  17  
16  17  18  0  0  0

让我们看一下copyOfRange(T [] original，int from，int to)和copyOfRange(U [] original，int from，int to，Class newType)的示例

// Java program to illustrate  
// copyOfRange method 
import java.util.Arrays; 
class GFG { 
    // User defined class 
    static class Employee { 
        int Eid; 
        String Ename; 
  
        // constructor 
    public Employee(int Eid, String Ename) 
        { 
            this.Eid = Eid; 
            this.Ename = Ename; 
        } 
  
        // Overide toString() 
    public String toString() 
        { 
            return Eid + "   " + Ename; 
        } 
    } 
  
    public static void
    main(String args[]) 
    { 
        Employee[] e = { new Employee(10, "geek1"), 
                         new Employee(20, "geek2"), 
                         new Employee(30, "geek3"), 
                         new Employee(40, "geek4"), 
                         new Employee(50, "geek5") }; 
  
        // Illustration of copyOfRange(T[] original, int from, int to) 
        // Working with user defined class 
        Employee[] getCopy_Employees = Arrays.copyOfRange(e, 3, 5); 
        for (Employee e1 : getCopy_Employees) 
            System.out.print(e1.toString() + "  "); 
  
        System.out.println(); 
  
        // IIlustration of copyOfRange(U[] original, int from, int to, Class newType) 
        // In this we store the user defined class Employee into Object class 
        // It Throws ArrayStoreException when we try to copy it in a class 
        // That is not correct 
        Object getcopy[] = Arrays.copyOfRange(e, 1, 3, Object[].class); 
  
        // This throws an error 
        // Number getcopy[] = Arrays.copyOfRange(e, 1, 3, Number[].class); 
  
        for (Object e1 : getcopy) { 
            System.out.print(e1.toString() + "  "); 
        } 
    } 
}

输出：

40   geek4  50   geek5  
20   geek2  30   geek3

copyOfvs copyOfRange

copyOf()开始从原始数组的第0个索引开始复制，并复制指定数量的元素
虽然copyOfRange()可以将元素范围复制到原始数组中。

参考：
docs.oracle.com/javase/8/docs/api/java/util/Arrays.html#copyOfRange-int:A-int-int-

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