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Access Protection:

Java provides four types access modifiers as public, private, default

and protected. Any variable declared as public, it could be accessed from
anywhere. Any variable declared as private cannot be seen outside of its
class. Any variable declared as default, it is visible to subclasses as well as
to other classes in the same package. Any variable declared as protected, it
allows an element to be seen outside of current package, but only to classes
that subclasses directly.

Package Access
Public Private Default protected
Location

Same class Yes Yes Yes Yes

sub class in Same

Yes No Yes Yes
package

non-subclass in Same
Yes No Yes Yes
package

sub class in Different

Yes No No Yes
package

non subclass in
Yes No No No
Different package
java.util.Date
The java.util.Date class represents date and time in java. It provides
constructors and methods to deal with date and time in java.

The java.util.Date class implements Serializable, Cloneable and

Comparable<Date> interface. It is inherited by java.sql.Date, java.sql.Time
and java.sql.Timestamp interfaces.

After Calendar class, most of the constructors and methods of java.util.Date

class has been deprecated. Here, we are not giving list of any deprecated
constructor and method.

java.util.Date Constructors

No. Constructor Description

1) Date() Creates a date object representing current date and

time.

2) Date(long Creates a date object for the given milliseconds

milliseconds) since January 1, 1970, 00:00:00 GMT.

java.util.Date Methods

No. Method Description

1) boolean after(Date date) tests if current date is after the given date.

2) boolean before(Date date) tests if current date is before the given date.

3) Object clone() returns the clone object of current date.

4) int compareTo(Date date) compares current date with given date.

5) boolean equals(Date date) compares current date with given date fo

equality.

6) static Date from(Instant returns an instance of Date object from Instan

instant) date.

7) long getTime() returns the time represented by this date object.

8) int hashCode() returns the hash code value for this date object.

9) void setTime(long time) changes the current date and time to given time.

10) Instant toInstant() converts current date into Instant object.

11) String toString() converts this date into Instant object.

java.util.Date Example
Let's see the example to print date in java using java.util.Date class.

1st way:

java.util.Date date=new java.util.Date();

System.out.println(date);
Test it Now

Output:

Wed Mar 27 08:22:02 IST 2015

2nd way:

long millis=System.currentTimeMillis();
java.util.Date date=new java.util.Date(millis);
System.out.println(date);
Test it Now

Output:

Wed Mar 27 08:22:02 IST 2015

java.util.Random

The java.util.Random class instance is used to generate a stream of pseudorandom

numbers.Following are the important points about Random −
 The class uses a 48-bit seed, which is modified using a linear congruential
formula.
 The algorithms implemented by class Random use a protected utility method that
on each invocation can supply up to 32 pseudorandomly generated bits.

Class declaration
Following is the declaration for java.util.Random class −
public class Random
extends Object
implements Serializable

Class constructors

Sr.No Constructor & Description

1
Random()
This creates a new random number generator.

2
Random(long seed)
This creates a new random number generator using a single long seed.

Class methods

Sr.No Method & Description

1 protected int next(int bits)

This method generates the next pseudorandom number.
2 boolean nextBoolean()
This method returns the next pseudorandom, uniformly distributed boolean
value from this random number generator's sequence.

3 void nextBytes(byte[] bytes)

This method generates random bytes and places them into a user-supplied
byte array.

4 double nextDouble()
This method returns the next pseudorandom, uniformly distributed double value
between 0.0 and 1.0 from this random number generator's sequence.

5 float nextFloat()
This method returns the next pseudorandom, uniformly distributed float value
between 0.0 and 1.0 from this random number generator's sequence.

6 double nextGaussian()
This method returns the next pseudorandom, Gaussian ("normally") distributed
double value with mean 0.0 and standard deviation 1.0 from this random
number generator's sequence.

7 int nextInt()
This method returns the next pseudorandom, uniformly distributed int value
from this random number generator's sequence.

8 int nextInt(int n)
This method returns a pseudorandom, uniformly distributed int value between 0
(inclusive) and the specified value (exclusive), drawn from this random number
generator's sequence.

9 long nextLong()
This method returns the next pseudorandom, uniformly distributed long value
from this random number generator's sequence.

10 void setSeed(long seed)

This method sets the seed of this random number generator using a single long
seed.
java.util.Arrays:

The java.util.Arrays class contains a static factory that allows arrays to be viewed as
lists.Following are the important points about Arrays −
 This class contains various methods for manipulating arrays (such as sorting and
searching).
 The methods in this class throw a NullPointerException if the specified array
reference is null.

Class declaration
Following is the declaration for java.util.Arrays class −
public class Arrays
extends Object

Class methods

Sr.No Method & Description

1 static <T> List<T> asList(T... a)

This method returns a fixed-size list backed by the specified array.

2 static int binarySearch(byte[] a, byte key)

This method searches the specified array of bytes for the specified value using
the binary search algorithm.

3 static int binarySearch(byte[] a, int fromIndex, int toIndex, byte key)

This method searches a range of the specified array of bytes for the specified
value using the binary search algorithm.

4 static int binarySearch(char[] a, char key)

This method searches the specified array of chars for the specified value using
the binary search algorithm.
5 static int binarySearch(char[] a, int fromIndex, int toIndex, char key)
This method searches a range of the specified array of chars for the specified
value using the binary search algorithm.

6 static int binarySearch(double[] a, double key)

This method searches the specified array of doubles for the specified value
using the binary search algorithm.

7 static int binarySearch(double[] a, int fromIndex, int toIndex, double key)

This method searches a range of the specified array of doubles for the
specified value using the binary search algorithm.

8 static int binarySearch(float[] a, float key)

This method searches the specified array of floats for the specified value using
the binary search algorithm.

9 static int binarySearch(float[] a, int fromIndex, int toIndex, float key)

This method searches a range of the specified array of floats for the specified
value using the binary search algorithm.

10 static int binarySearch(int[] a, int key)

This method searches the specified array of ints for the specified value using
the binary search algorithm.

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

This method searches a range of the specified array of ints for the specified
value using the binary search algorithm.

12 static int binarySearch(long[] a, int fromIndex, int toIndex, long key)

This method searches a range of the specified array of longs for the specified
value using the binary search algorithm.

13 static int binarySearch(long[] a, long key)

This method searches the specified array of longs for the specified value using
the binary search algorithm.

14 static int binarySearch(Object[] a, int fromIndex, int toIndex, Object key)

This method searches a range of the specified array for the specified object
using the binary search algorithm.

15 static int binarySearch(Object[] a, Object key)

This method searches the specified array for the specified object using the
binary search algorithm.

16 static int binarySearch(short[] a, int fromIndex, int toIndex, short key)

This method searches a range of the specified array of shorts for the specified
value using the binary search algorithm.

17 static int binarySearch(short[] a, short key)

This method searches the specified array of shorts for the specified value using
the binary search algorithm.

18 static <T> int binarySearch(T[] a, int fromIndex, int toIndex, T key, Comparator<?
super T> c)
This method searches a range of the specified array for the specified object
using the binary search algorithm.

19 static <T> int binarySearch(T[] a, T key, Comparator<? super T> c)

This method searches the specified array for the specified object using the
binary search algorithm.

20 static boolean[] copyOf(boolean[] original, int newLength)

This method copies the specified array, truncating or padding with false (if
necessary) so the copy has the specified length.

21 static byte[] copyOf(byte[] original, int newLength)

This method copies the specified array, truncating or padding with zeros (if
necessary) so the copy has the specified length.

22 static char[] copyOf(char[] original, int newLength)

This method copies the specified array, truncating or padding with null
characters (if necessary) so the copy has the specified length.

23 static double[] copyOf(double[] original, int newLength)

This method copies the specified array, truncating or padding with zeros (if
necessary) so the copy has the specified length.

24 static float[] copyOf(float[] original, int newLength)

This method copies the specified array, truncating or padding with zeros (if
necessary) so the copy has the specified length.

25 static int[] copyOf(int[] original, int newLength)

This method copies the specified array, truncating or padding with zeros (if
necessary) so the copy has the specified length.

26 static long[] copyOf(long[] original, int newLength)

This method copies the specified array, truncating or padding with zeros (if
necessary) so the copy has the specified length.

27 static short[] copyOf(short[] original, int newLength)

This method copies the specified array, truncating or padding with zeros (if
necessary) so the copy has the specified length.

28 static <T> T[] copyOf(T[] original, int newLength)

This method copies the specified array, truncating or padding with nulls (if
necessary) so the copy has the specified length.

29 static <T,U> T[] copyOf(U[] original, int newLength, Class<? extends T[]>
newType)
This method copies the specified array, truncating or padding with nulls (if
necessary) so the copy has the specified length.

30 static boolean[] copyOfRange(boolean[] original, int from, int to)

This method copies the specified range of the specified array into a new array.

31 static byte[] copyOfRange(byte[] original, int from, int to)

This method copies the specified range of the specified array into a new array.

32 static char[] copyOfRange(char[] original, int from, int to)

This method copies the specified range of the specified array into a new array.
33 static double[] copyOfRange(double[] original, int from, int to)
This method copies the specified range of the specified array into a new array.

34 static float[] copyOfRange(float[] original, int from, int to)

This method copies the specified range of the specified array into a new array.

35 static int[] copyOfRange(int[] original, int from, int to)

This method copies the specified range of the specified array into a new array.

36 static long[] copyOfRange(long[] original, int from, int to)

This method copies the specified range of the specified array into a new array.

37 static short[] copyOfRange(short[] original, int from, int to)

This method copies the specified range of the specified array into a new array.

38 static <T> T[] copyOfRange(T[] original, int from, int to)

This method copies the specified range of the specified array into a new array.

39 static <T,U> T[] copyOfRange(U[] original, int from, int to, Class<? extends T[]>
newType)
This method copies the specified range of the specified array into a new array.

40 static boolean deepEquals(Object[] a1, Object[] a2)

This method returns true if the two specified arrays are deeply equal to one
another.

41 static int deepHashCode(Object[] a)

This method returns a hash code based on the "deep contents" of the specified
array.

42 static String deepToString(Object[] a)

This method returns a string representation of the "deep contents" of the
specified array.

43 static boolean equals(boolean[] a, boolean[] a2)

This method returns true if the two specified arrays of booleans are equal to
one another.

44 static boolean equals(byte[] a, byte[] a2)

This method returns true if the two specified arrays of bytes are equal to one
another.

45 static boolean equals(char[] a, char[] a2)

This method returns true if the two specified arrays of chars are equal to one
another.

46 static boolean equals(double[] a, double[] a2)

This method returns true if the two specified arrays of doubles are equal to one
another.

47 static boolean equals(float[] a, float[] a2)

This method returns true if the two specified arrays of floats are equal to one
another.

48 static boolean equals(int[] a, int[] a2)

This method returns true if the two specified arrays of ints are equal to one
another.

49 static boolean equals(long[] a, long[] a2)

This method returns true if the two specified arrays of longs are equal to one
another.

50 static boolean equals(Object[] a, Object[] a2)

This method returns true if the two specified arrays of Objects are equal to one
another.

51 static boolean equals(short[] a, short[] a2)

This method returns true if the two specified arrays of shorts are equal to one
another.

52 static void fill(boolean[] a, boolean val)

This method assigns the specified boolean value to each element of the
specified array of booleans.
53 static void fill(boolean[] a, int fromIndex, int toIndex, boolean val)
This method assigns the specified boolean value to each element of the
specified range of the specified array of booleans.

54 static void fill(byte[] a, byte val)

This method assigns the specified byte value to each element of the specified
array of bytes.

55 static void fill(byte[] a, int fromIndex, int toIndex, byte val)

This method assigns the specified byte value to each element of the specified
range of the specified array of bytes.

56 static void fill(char[] a, char val)

This method assigns the specified char value to each element of the specified
array of chars.

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

This method assigns the specified char value to each element of the specified
range of the specified array of chars.

58 static void fill(double[] a, double val)

This method assigns the specified double value to each element of the
specified array of doubles.

59 static void fill(double[] a, int fromIndex, int toIndex, double val)

This method assigns the specified double value to each element of the
specified range of the specified array of doubles.

60 static void fill(float[] a, float val)

This method assigns the specified float value to each element of the specified
array of floats.

61 static void fill(float[] a, int fromIndex, int toIndex, float val)

This method assigns the specified float value to each element of the specified
range of the specified array of floats.

62 static void fill(int[] a, int val)

This method assigns the specified int value to each element of the specified
array of ints.

63 static void fill(int[] a, int fromIndex, int toIndex, int val)

This method assigns the specified int value to each element of the specified
range of the specified array of ints.

64 static void fill(long[] a, int fromIndex, int toIndex, long val)

This method assigns the specified long value to each element of the specified
range of the specified array of longs.

65 static void fill(long[] a, long val)

This method assigns the specified long value to each element of the specified
array of longs.

66 static void fill(Object[] a, int fromIndex, int toIndex, Object val)

This method assigns the specified Object reference to each element of the
specified range of the specified array of Objects.

67 static void fill(Object[] a, Object val)

This method assigns the specified Object reference to each element of the
specified array of Objects.

68 static void fill(short[] a, int fromIndex, int toIndex, short val)

This method assigns the specified short value to each element of the specified
range of the specified array of shorts.