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Advanced Programming

with Java

Strings and Arrays

Oranit Dror and Ohad Barzilay

Advanced Java ProgrammingTel Aviv University

2

TheThe StringString ClassClass

Represents a character string (e.g. "Hi")

Implicit constructor:

String quote = "Hello World";

All string literals are String instances

Object has a toString() method

More details in JDK 5.0 documentation

http://java.sun.com/j2se/1.5.0/docs/

string literal

Advanced Java Programming

Tel Aviv University

3

String ImmutabilityString Immutability

Strings are constantsString s = " Tea ";

s = s.trim();

s = s.replace('T', 'S');

A string reference may be set:String s = "Tea";

s = "Sea";Advanced Java Programming

Tel Aviv University

4

String InterningString Interning

Avoids duplicate stringsString[] array = new String[1000];

for (int i=0 ; i

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Advanced Java ProgrammingTel Aviv University

13

More efficient version with StringBuffer:

public static String

duplicate(String s, int times) {StringBuffer result = new StringBuffer(s);

for (int i=1; i

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Advanced Java ProgrammingTel Aviv University

19

Array Creation and InitializationArray Creation and Initialization

Creating and initializing small arrayswith a-prioriknown values:

int[] odds = {1,3,5,7,9,11,13,15};

String months[] =

{"Jan", "Feb", "Mar", "Apr","May", "Jun", "July", "Aug","Sep", "Oct", "Nov", "Dec"};

Jan

String Pool

months:

Advanced Java ProgrammingTel Aviv University

20

Loop through ArraysLoop through Arrays

By promoting the array's index:

for (int i=0 ; i < months.length ; i++) {

System.out.println(months[i]);

}

In Java 5.0:

for (String month: months) {

System.out.println(month);

}

The variable month is assignedthe next element in each iteration

Advanced Java Programming

Tel Aviv University

21

Manipulating arraysManipulating arrays

The java.util.Arrays class has methods for

sorting and searching arrays e.g. public static void sort(int[] a)

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

In the java.lang.System class: public static void arraycopy(Object src, int srcPos,

Object dest, int destPos,

int length)

Advanced Java Programming

Tel Aviv University

22

Copying ArraysCopying Arrays

Nave copy:

int vec1[] = {1,2,3};

int vec2[] = {8,7,6,5};

vec1 = vec2;

Doing it by hand is

inefficient arraycopy(vec2, 0, vec1, 0, 3);

will replace 1,2,3 in vec1 with 8,7,6

Advanced Java Programming

Tel Aviv University

23

Manipulating arrays (cont.)Manipulating arrays (cont.)

What is the output of the following code:int[] odds = {1,3,5,7,9,11,13,15};

int[] newOdds = new int[8];System.arraycopy(odds, 1, newOdds, 1, 7);

for (int odd: odds) {

System.out.print(odd + " ");

}

Output:0 3 5 7 9 11 13 15

Advanced Java Programming

Tel Aviv University

24

Reading command line argumentsReading command line arguments

class CommandLineDemo

{

public static voidmain(String args[])

{

for (int i=0; i java CommandLineDemo Apple Box Car

Argument number 1 is : Apple

Argument number 2 is : Box

Argument number 3 is : Car

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Advanced Java ProgrammingTel Aviv University

25

2 Dimensional Arrays

There are no 2D arrays in Java but you canbuild array of arrays:

char[] board[] = new char[3][];for (int i = 0; i