java的数组与Arrays类源码详解

java的数组与Arrays类源码详解

　　java.util.Arrays 类是 JDK 提供的一个工具类，用来处理数组的各种方法，而且每个方法基本上都是静态方法，能直接通过类名Arrays调用。

类的定义

public final
class Array {

    private Array() {}

    public static Object newInstance(Class componentType, int length)
        throws NegativeArraySizeException {
        return newArray(componentType, length);
    }

    public static Object newInstance(Class componentType, int... dimensions)
        throws IllegalArgumentException, NegativeArraySizeException {
        return multiNewArray(componentType, dimensions);
    }

    public static native int getLength(Object array)
        throws IllegalArgumentException;

    public static native Object get(Object array, int index)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native boolean getBoolean(Object array, int index)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    
    public static native byte getByte(Object array, int index)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native char getChar(Object array, int index)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native short getShort(Object array, int index)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native int getInt(Object array, int index)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native long getLong(Object array, int index)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native float getFloat(Object array, int index)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native double getDouble(Object array, int index)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native void set(Object array, int index, Object value)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native void setBoolean(Object array, int index, boolean z)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native void setByte(Object array, int index, byte b)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native void setChar(Object array, int index, char c)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native void setShort(Object array, int index, short s)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native void setInt(Object array, int index, int i)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native void setLong(Object array, int index, long l)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native void setFloat(Object array, int index, float f)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;

    public static native void setDouble(Object array, int index, double d)
        throws IllegalArgumentException, ArrayIndexOutOfBoundsException;


    private static native Object newArray(Class componentType, int length)
        throws NegativeArraySizeException;

    private static native Object multiNewArray(Class componentType,
        int[] dimensions)
        throws IllegalArgumentException, NegativeArraySizeException;


}

java.lang.reflect.Array.setChar(Object array, int index, double value)方法将指定数组对象的索引组件的值设置为指定的double值。

import java.lang.reflect.Array;

public class ArrayDemo {
   public static void main(String[] args) {
      double[] array = new double[]{1.0,2.0,3.0};

      Array.setDouble(array, 0, 2.0);
      Array.setDouble(array, 1, 3.0);
      Array.setDouble(array, 2, 4.0);

      System.out.println("array[0] = " + Array.getDouble(array, 0));
      System.out.println("array[1] = " + Array.getDouble(array, 1));
      System.out.println("array[2] = " + Array.getDouble(array, 2));
   }
}

编译并运行上面的程序，将产生以下结果 -

array[0] = 2.0
array[1] = 3.0
array[2] = 4.0

Arrays类的定义

public class Arrays {

    private static final int MIN_ARRAY_SORT_GRAN = 1  toIndex) {
            throw new IllegalArgumentException(
                    "fromIndex(" + fromIndex + ") > toIndex(" + toIndex + ")");
        }
        if (fromIndex < 0) {
            throw new ArrayIndexOutOfBoundsException(fromIndex);
        }
        if (toIndex > arrayLength) {
            throw new ArrayIndexOutOfBoundsException(toIndex);
        }
    }

    public static void sort(int[] a) {
        DualPivotQuicksort.sort(a, 0, a.length - 1, null, 0, 0);
    }

    public static void sort(int[] a, int fromIndex, int toIndex) {
        rangeCheck(a.length, fromIndex, toIndex);
        DualPivotQuicksort.sort(a, fromIndex, toIndex - 1, null, 0, 0);
    }

    public static void sort(long[] a) {
        DualPivotQuicksort.sort(a, 0, a.length - 1, null, 0, 0);
    }

    public static void sort(long[] a, int fromIndex, int toIndex) {
        rangeCheck(a.length, fromIndex, toIndex);
        DualPivotQuicksort.sort(a, fromIndex, toIndex - 1, null, 0, 0);
    }

    public static void sort(short[] a) {
        DualPivotQuicksort.sort(a, 0, a.length - 1, null, 0, 0);
    }

    public static void sort(short[] a, int fromIndex, int toIndex) {
        rangeCheck(a.length, fromIndex, toIndex);
        DualPivotQuicksort.sort(a, fromIndex, toIndex - 1, null, 0, 0);
    }

    public static void sort(char[] a) {
        DualPivotQuicksort.sort(a, 0, a.length - 1, null, 0, 0);
    }

    public static void sort(char[] a, int fromIndex, int toIndex) {
        rangeCheck(a.length, fromIndex, toIndex);
        DualPivotQuicksort.sort(a, fromIndex, toIndex - 1, null, 0, 0);
    }

    public static void sort(byte[] a) {
        DualPivotQuicksort.sort(a, 0, a.length - 1);
    }

    public static void sort(byte[] a, int fromIndex, int toIndex) {
        rangeCheck(a.length, fromIndex, toIndex);
        DualPivotQuicksort.sort(a, fromIndex, toIndex - 1);
    }

    public static void sort(float[] a) {
        DualPivotQuicksort.sort(a, 0, a.length - 1, null, 0, 0);
    }

    public static void sort(float[] a, int fromIndex, int toIndex) {
        rangeCheck(a.length, fromIndex, toIndex);
        DualPivotQuicksort.sort(a, fromIndex, toIndex - 1, null, 0, 0);
    }

    public static void sort(double[] a) {
        DualPivotQuicksort.sort(a, 0, a.length - 1, null, 0, 0);
    }

    public static void sort(double[] a, int fromIndex, int toIndex) {
        rangeCheck(a.length, fromIndex, toIndex);
        DualPivotQuicksort.sort(a, fromIndex, toIndex - 1, null, 0, 0);
    }

    public static void parallelSort(byte[] a) {
        int n = a.length, p, g;
        if (n  eClass = element.getClass();

                if (eClass.isArray()) {
                    if (eClass == byte[].class)
                        buf.append(toString((byte[]) element));
                    else if (eClass == short[].class)
                        buf.append(toString((short[]) element));
                    else if (eClass == int[].class)
                        buf.append(toString((int[]) element));
                    else if (eClass == long[].class)
                        buf.append(toString((long[]) element));
                    else if (eClass == char[].class)
                        buf.append(toString((char[]) element));
                    else if (eClass == float[].class)
                        buf.append(toString((float[]) element));
                    else if (eClass == double[].class)
                        buf.append(toString((double[]) element));
                    else if (eClass == boolean[].class)
                        buf.append(toString((boolean[]) element));
                    else { // element is an array of object references
                        if (dejaVu.contains(element))
                            buf.append("[...]");
                        else
                            deepToString((Object[])element, buf, dejaVu);
                    }
                } else {  // element is non-null and not an array
                    buf.append(element.toString());
                }
            }
            if (i == iMax)
                break;
            buf.append(", ");
        }
        buf.append(']');
        dejaVu.remove(a);
    }

toString 用来打印一维数组的元素，而 deepToString 用来打印多层次嵌套的数组元素。