深入了解Java核心类库--Arrays类

int [] a1 = { 1 , 2 , 3 , 4 , 5 };

System.out.println(Arrays.toString(a1)); //[1, 2, 3, 4, 5]

public static String toString( int [] a) {

     if (a == null )

         return "null" ;

     int iMax = a.length - 1 ;

     if (iMax == - 1 )

         return "[]" ;

     StringBuilder b = new StringBuilder();

     b.append( '[' );

     for ( int i = 0 ; ; i++) {

         b.append(a[i]);

         if (i == iMax)

             return b.append( ']' ).toString();

         b.append( ", " );

     }

}

int [] a1 = { 9 , 1 , 3 , 7 , 2 , 5 };

System.out.println(Arrays.toString(a1)); //[9, 1, 3, 7, 2, 5]

Arrays.sort(a1, 0 , 3 ); //[0,3),对9,1,3进行排序

System.out.println(Arrays.toString(a1)); //[0[1, 3, 9, 7, 2, 5]

public static void sort( int [] a, int fromIndex, int toIndex) {

     rangeCheck(a.length, fromIndex, toIndex);

     DualPivotQuicksort.sort(a, fromIndex, toIndex - 1 , null , 0 , 0 );

}

int [] a1 = { 0 , 7 , 8 , 2 , 4 , 1 };

System.out.println(Arrays.toString(a1)); //[0, 7, 8, 2, 4, 1]

Arrays.sort(a1);

System.out.println(Arrays.toString(a1)); //[0, 1, 2, 4, 7, 8]

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

}

int [] a = { 1 , 2 , 3 };

System.out.println(a.length); //output：3

a = Arrays.copyOf(a, 15 );

System.out.println(a.length); //output：15

public static int [] copyOf( int [] original, int newLength) {

       int [] copy = new int [newLength];

       System.arraycopy(original, 0 , copy, 0 , Math.min(original.length, newLength));

       return copy;

   }

int [] a1 = { 0 , 1 , 2 , 3 , 4 , 5 };

int [] a2 = { 0 , 1 , 2 , 3 , 4 , 5 }; //与a1相同

int [] a3 = { 0 , 1 , 2 , 3 , 0 , 5 }; //从索引4开始与a1不同

System.out.println(Arrays.mismatch(a1,a2)); //output：-1

System.out.println(Arrays.mismatch(a1,a3)); //output：4

public static int mismatch( int [] a, int [] b) {

        int length = Math.min(a.length, b.length); // Check null array refs

        if (a == b)

            return - 1 ;

        int i = ArraysSupport.mismatch(a, b, length);

        return (i < 0 && a.length != b.length) ? length : i;

    }

int [] a = { 1 , 2 , 3 , 4 , 5 };

      int x1 = Arrays.binarySearch(a, 2 , 3 , 4 ); //在a数组下标[2,3)中查找值为4的下标

      System.out.println(x1); //output：<0的随机数

public static int binarySearch( int [] a, int fromIndex, int toIndex, int key) {

     rangeCheck(a.length, fromIndex, toIndex);

     return binarySearch0(a, fromIndex, toIndex, key);

}

private static int binarySearch0( int [] a, int fromIndex, int toIndex, int key) {

     int low = fromIndex;

     int high = toIndex - 1 ;

     while (low <= high) {

         int mid = (low + high) >>> 1 ;

         int midVal = a[mid];

         if (midVal < key)

             low = mid + 1 ;

         else if (midVal > key)

             high = mid - 1 ;

         else

             return mid; // key found

     }

     return -(low + 1 );  // key not found.

}

int [] a = { 1 , 2 , 3 , 4 , 5 };

int x1 = Arrays.binarySearch(a, 3 ); //在a数组中查找值为3的下标

int x2 = Arrays.binarySearch(a,- 6 ); //在a数组中查找值为6的下标

System.out.println(x1); //output：2

System.out.println(x2); //output：<0的随机数

public static int binarySearch( int [] a, int key) {

     return binarySearch0(a, 0 , a.length, key);

}

private static int binarySearch0( int [] a, int fromIndex, int toIndex, int key) {

     int low = fromIndex;

     int high = toIndex - 1 ;

     while (low <= high) {

         int mid = (low + high) >>> 1 ;

         int midVal = a[mid];

         if (midVal < key)

             low = mid + 1 ;

         else if (midVal > key)

             high = mid - 1 ;

         else

             return mid; // key found

     }

     return -(low + 1 );  // key not found.

}

int [] a1 = { 1 , 2 , 3 , 4 , 5 };

int [] a2 = { 1 , 2 , 0 , 0 , 4 , 5 };

System.out.println(Arrays.equals(a1, 0 , 2 ,a2, 0 , 2 )); //true

System.out.println(Arrays.equals(a1, 3 , 5 ,a2, 4 , 6 )); //true

public static boolean equals( int [] a, int aFromIndex, int aToIndex, int [] b, int bFromIndex, int bToIndex) {

         rangeCheck(a.length, aFromIndex, aToIndex);

         rangeCheck(b.length, bFromIndex, bToIndex);

         int aLength = aToIndex - aFromIndex;

         int bLength = bToIndex - bFromIndex;

         if (aLength != bLength)

             return false ;

         return ArraysSupport.mismatch(a, aFromIndex, b, bFromIndex,aLength) < 0 ;

     }

int [] a1 = { 1 , 2 , 3 , 4 , 5 };

int [] a2 = { 1 , 2 , 3 , 4 , 5 };

int [] a3 = { 1 , 2 , 0 , 4 , 5 };

System.out.println(Arrays.equals(a1,a2)); //true

System.out.println(Arrays.equals(a1,a3)); //false

public static boolean equals( int [] a, int [] a2) {

        if (a==a2)

            return true ;

        if (a== null || a2== null )

            return false ;

        int length = a.length;

        if (a2.length != length)

            return false ;

        return ArraysSupport.mismatch(a, a2, length) < 0 ;

    }

int [] a1 = new int [ 10 ];

Arrays.fill(a1, 1 , 4 , 8 );

char [] a2 = new char [ 10 ];

Arrays.fill(a2, 0 , 3 , 's' );

System.out.println(Arrays.toString(a1)); //[0, 8, 8, 8, 0, 0, 0, 0, 0, 0]

System.out.println(Arrays.toString(a2)); //[s, s, s,  ,  ,  ,  ,  ,  ,  ]

public static void fill( char [] a, int fromIndex, int toIndex, char val) {

     rangeCheck(a.length, fromIndex, toIndex);

     for ( int i = fromIndex; i < toIndex; i++)

         a[i] = val;

}

int [] a1 = new int [ 10 ];

Arrays.fill(a1, 8 );

char [] a2 = new char [ 10 ];

Arrays.fill(a2, 's' );

System.out.println(Arrays.toString(a1)); //[8, 8, 8, 8, 8, 8, 8, 8, 8, 8]

System.out.println(Arrays.toString(a2)); //[s, s, s, s, s, s, s, s, s, s]

public static void fill( int [] a, int val) {

     for ( int i = 0 , len = a.length; i < len; i++)

         a[i] = val;

}