Data structures
Object-Oriented Programming
Outline
Primitive data types
String
Math class
Array
Container classes
Readings:
HFJ: Ch. 13, 6.
GT: Ch. 13, 6.
i hc Cng ngh - HQG HN
Data structures
Basic classes
Object
Boolean
Character
Byte
i hc Cng ngh - HQG HN
Short
Void
Number
Integer
Math
Long
Data structures
String
StringBuffer ...
Float
Double
The Object class
Class getClass() returns class name of the current objects.
Cat a = new Cat(Tom);
Class c = a.getClass();
System.out.println(c);
boolean equals(Object) compares objects, is usually
redefined.
String toString() returns text representation of the object,
is usually redefined.
i hc Cng ngh - HQG HN
Data structures
Primitive data types
Utility methods:
valueOf(String s) returns an object of the corresponding type
holding the value of String s.
Integer k = Integer.valueOf( "12"); // k = 12
typeValue() returns primitive value of the object
int i = k.intValue();
// i = 12
static parseType(String s) converts a string into a value of
the corresponding primitive type
int i = Integer.parseInt("12");
// i = 12
constants
Type.MAX_VALUE, Type.MIN_VALUE
i hc Cng ngh - HQG HN
Data structures
The Character class
Methods
static
static
static
static
static
static
static
boolean isUppercase(char ch)
boolean isLowercase(char ch)
boolean isDigit(char ch)
boolean isLetter(char ch)
boolean isLetterOrDigit(char ch)
char toUpperCase(char ch)
char toLowerCase(char ch)
i hc Cng ngh - HQG HN
Data structures
The String class
String: unmodifiable sequence of characters.
Initialise:
String(String)
String(StringBuffer)
String(byte[])
String(char[])
Methods
int length the length of the string
char charAt(int index) returns the character at position
index
i hc Cng ngh - HQG HN
Data structures
The String class
Comparison
boolean equals(String)
boolean equalsIgnoreCase(String)
boolean startWith(String)
boolean endWith(String)
int compareTo(String)
Conversion
String toUpperCase()
String toLowerCase()
Concatenation
String concat(String)
operator +
i hc Cng ngh - HQG HN
Data structures
The String class
Search forwards
int indexOf(int ch)
int indexOf(int ch, int from)
int indexOf(String)
int indexOf(String s, int from)
Search backwards
int lastIndexOf(int ch)
int lastIndexOf(int ch, int from)
int lastIndexOf(String)
int lastIndexOf(String, int)
i hc Cng ngh - HQG HN
Data structures
The String class
Replace
String replace(char oldChar, char newChar)
returns a new string resulting from replacing all
occurrences of oldChar with newChar
Substring
String trim() returns a copy of the string, with leading
and trailing white space omitted.
String substring(int startIndex)
String substring(int start, int end)
i hc Cng ngh - HQG HN
Data structures
10
StringBuffer
StringBuffer: modifiable sequence of characters
Initialize
StringBuffer(String)
StringBuffer(int length)
StringBuffer(): default size is 16
Utilities
int length()
void setLength()
char charAt(int index)
void setCharAt(int index, char ch)
String toString()
i hc Cng ngh - HQG HN
Data structures
11
StringBuffer
Edit
append(String)
append(type t) appends t's string representation
insert(int offset, String s)
insert(int offset, char[] chs)
insert(int offset, type t)
delete(int start, int end) deletes a substring
delete(int index) deletes 01 character
reverse()
i hc Cng ngh - HQG HN
Data structures
12
The Math class
Constants
Math.E
Math.PI
Static methods
type abs(type): absolute value of int/double/long
double ceil(double)
double floor(double)
int round(float)
long round(double)
type max(type, type), type min(type, type)
i hc Cng ngh - HQG HN
Data structures
13
The Math class
Static methods (cont.)
double random() generates random value in the range [0.0,1.0]
double pow(double, double)
double exp(double) e raised to the power of a value.
double log(double) natural logarithm (base e)
double sqrt(double)
trigonometric
double sin(double) returns sine of an angle
double cos(double) returns cosine of an angle
double tan(double) returns tangent of an angle
i hc Cng ngh - HQG HN
Data structures
14
Array
An array is an object that
contains a set of objects
must be created (new) before use
int
a =
for
for
a[];
new int[10];
(int i = 0; i < a.length; i++) a[i] = i * i;
(int w: a)
System.out.print(w + " ");
int b[] = {2, 3, 5, 7};
a = b;
int m, n[];
double[] arr1, arr2;
i hc Cng ngh - HQG HN
Data structures
15
Array as argument and return value
int[] myCopy(int[] a)
{
int b[] = new int[a.length];
for (i=0; i<a.length; i++)
b[i] = a[i];
return b;
}
...
int a[] = {0, 1, 1, 2, 3, 5, 8};
int b[] = myCopy(a);
i hc Cng ngh - HQG HN
Data structures
16
Multi-dimensional arrays
int a[][];
a = new int[10][20];
a[2][3] = 10;
for (int i=0; i<a[0].length; i++)
a[0][i] = i;
for (int w: a[0])
System.out.print(w + " ");
int b[][] = { {1 , 2}, {3, 4} };
int c[][] = new int[2][];
c[0] = new int[5];
c[1] = new int[10];
i hc Cng ngh - HQG HN
Data structures
17
Array copy
System.arraycopy(src, s_off, des, d_off, len)
src: source array, s_off: source array's offset
des: destination array, d_off: destination array's offset
len: number of entries to be copied
Entries's content is copied
Primitive value
Object reference.
i hc Cng ngh - HQG HN
Data structures
18
The Array class
In the package java.util
Four static methods
fill() initialises array entries with one same value
sort() sorts array
works with arrays of primitive values
works with classes that implement Comparable
equals() compares two arrays
binarySearch() performs binary search in sorted arrays,
creates logic error if used for unsorted arrays.
i hc Cng ngh - HQG HN
Data structures
19
Container classes
<< interface>>
Map
<< interface>>
Collection
HashMap
HashTable
<< interface>>
Set
<< interface>>
Sorted Map
<< interface>>
List
Tree Map
HashSet
<< interface>>
Sorted Set
Array List
Vector
LinkedList
TreeSet
i hc Cng ngh - HQG HN
Data structures
20
Iterator
An iterator allows a program to walk through a
collection and remove elements from the collection
during the iteration.
Java Iterator interface
hasNext()
next()
remove()
Collection classes implement Iterator
i hc Cng ngh - HQG HN
Data structures
21
import java.util.*;
public class TestList {
static public void main(String args[])
{
Collection list = new LinkedList();
list.add(3);
list.add(2);
list.add(1);
list.add(0);
list.add("go!");
3
2
1
0
go!
Iterator i = list.iterator();
while (i.hasNext()) {
System.out.println(i.next());
}
}
}
i hc Cng ngh - HQG HN
Data structures
22
import java.util.*;
public class TestList {
static public void main(String args[])
{
List list = new LinkedList();
list.add(3);
list.add(2);
list.add(1);
list.add(0);
list.add("go!");
3
2
1
0
go!
for (int i=0; i<list.size(); i++) {
System.out.println(list.get(i));
}
}
}
i hc Cng ngh - HQG HN
Data structures
23
import java.util.*;
public class TestList {
static public void main(String args[])
{
List<Integer> list = new LinkedList<Integer>();
list.add(3);
list.add(2);
list.add(1);
list.add(0);
//list.add("go!");
3
2
1
0
for (int i=0; i<list.size(); i++) {
System.out.println(list.get(i));
}
}
}
i hc Cng ngh - HQG HN
Data structures
24
