Zaawansowane programowanie obiektowe

Lecture 1

Szymon Grabowskisgrabow@kis.p.lodz.pl

http://szgrabowski.kis.p.lodz.pl/zpo11/

Łódź, 2011

2

Recommended literature / resources

Bruce Eckel, Thinking in Java, Prentice Hall, 2006 (4th Ed.).

http://download.oracle.com/javase/tutorial/index.html

Cay S. Horstmann, Gary Cornell, Core Java 2 : Volume I – Fundamentals; Volume II – Advanced Features,

Prentice Hall, 2007 (8th Edition).

http://www.horstmann.com/corejava/corejava8.zip

In Polish: Java. Podstawy. Wyd. VIII, 2008 (Helion), Java. Techniki zaawansowane. Wydanie VIII, 2009 (Helion).

Paul Deitel, Harvey Deitel, Java for Programmers. Second Edition, Prentice Hall, 2011.

Krzysztof Barteczko, Java od podstaw do techologii, tom 1 i 2, Mikom, 2004 (in Polish).

In Polish: http://jacenty.kis.p.lodz.pl/systemy_multimedialne.html

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A little bit of history

Developed by Sun in 1995. Based on C++.

Versions: 1.0.x, 1.1.x etc. up to SE 7 now (since July 2011).

(Don't get confused: everything from v1.2+ is Java 2.)

Java 2 in three editions: standard (SE), enterprise (EE) and micro (ME).

For example, J2ME is for PDA’s (e.g. cell phones) –lighter.

Android SDK: new platform, old (Java) language.

4

Design goals

Portability (running on a Java Virtual Machine).

High-level (objects, threads, exceptions, interfaces, packages, native zip handling...).

Rich standard library (GUI, DB support, regexp, algorithms and data structures).

Basically, there are three kinds of Java applications:

• applets (interpreted and run by a web browser, on the client side);

• servlets (on the server side);

• stand-alone apps.

5

What makes Java safe

Garbage collector.(No delete for objects, arrays...

Objects no longer used will be deallocatedautomatically.)

Exceptions everywhere. (In C++ they were optional.Here they are mandatory.)

Applets – sandbox model.(Some operations not allowed, unless perhaps

the applet’s digital signature is approved.)

References, no (explicit) pointers.

Strong typing. No implicit conversions (except some safe cases, see later), no int boolean conversion.

6

What makes Java slow

See previous slide...

But also, and this is the most important speed penalty factor, the thing that

Java is interpreted by a JVM.

7

Java vs. C++, main differences (summary)

Removed in Java:• preprocessor (#define, #include etc.)

• operator overloading

• (explicit) pointers

• typedef

• standalone functions; global variables

• multiple inheritance

• non-virtual methods.

Added in Java:• interfaces

• garbage collector

• array bound checking, strong typing

• concurrency support.

8

Create & run Java code[ http://ww2.cs.fsu.edu/~pfenning ]

Five stages:

1. Edit – creating .java file

2. Compile – creating .class files (one .class file per built class). This is B-code

(cmd-line: javac MyClass.java)

3. Load – loading bytecodes into memory

4. Verify – confirm bytecode validity and that it is secure

5. Execute – program execution (cmd-line: java MyClass – don’t type the extension)

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Formatted output[ http://mcsp.wartburg.edu/zelle/python/ccsc-html/mgp00005.html ]

No longer needed since J2SE 5.0 !

Use System.out.printf

("%10.2f", x);

10

Math ops – like in C (mostly)

+, -, *, /, %, +=, /=, ++ (prefix and postfix) etc.

==, !=, <= etc. (returns true or false)

int a = 10; // assignment

Ternary op (like in C), example:System.out.println(height>=185 ? "Tall" : height>=170 ?

"Medium" : "Short");

Examples:

int total = 5;int current = 4;total *= current + 3; // result?

int x = 5, y = 7;int result = x++ * --y; // result?Don’t do it. Correct (if x, y small enough ints not to overflow!), but obscure code.

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Java-specific math operators

&& and || are like in C; they use short-circuit (aka lazy) evaluation, e.g.

boolean cond = false;int x = 4;if (cond && x > 5) ... // cond – false the whole expression is false

// i.e. (x>5) will not be evaluated

But & and | for booleans mean almost the same, except for full evaluation.

Beware: in C/C++ the operators & and | are AND/OR on the bitwise level!

In Java, bitwise &, | and ^ (xor) still exist though.E.g. int n = 10 & 6 | 5; // n==7

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Java-specific math operators, cont’d

Other bitwise ops:~ (negation), << (shift left), >> (shift right), <<=, >>=,

>>>, >>>= (no equivalence in C/C++)

>>> is unsigned shift right:regardless of the sign, zeroes are inserted at the

higher-order bits.

But the signed right shift >> uses sign extension: if the value is positive, 0s are inserted at the higher-order bits; if the value is negative, 1s are inserted at the higher-order bits.

Example:

int a = -11;PrintStream so = System.out; so.println(a >> 1); // -6so.println(a >>> 1); // 2147483642

a = 11; so.println(a >> 1); // 5so.println(a >>> 1); // 5

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8 primitive data types

char (single characters in Unicode, 2 bytes!,from '\u0000' to '\uffff')

boolean (true or false; 1 byte)

integer types (all signed):byte (8 bits)

short (16 bits)int (32 bits)

long (64 bits)

floating point types:float (32 bits)

double (64 bits)

No unsigned types in Java!

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Built-in data types, examples

float x=3.5F, y=-5.92F, z;

int n1 = 54;

boolean trustworthy = false;

char c = '\u1f00';

long theKeyToUniverse = 42353265264254219L;

final double PI = 3.14; // keyword final means a constant!

Printing variables:

int x = 3;

System.out.println("x is now " + x + ", isn't it?");

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Arrays, quick remainder (1 / 2)

Indexes from 0. Same element type in a whole array.Stored in consecutive memory cells (hence O(1) access).

Arrays may be passed to methods and returned from methods.

Creating an array:int[] tab; // declare the arraytab = new int[100]; // create the arraytab[tab.length-1] = 5; // set the last item to 5

tab[tab.length] = 8; // IndexOutOfBoundsException!int[10] arr; // compile-time error!

Create and initiate:int[] n = {10, 20, 30, 40}; // or: … = new int[]{10, 20, 30, 40};

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Multi-dim arrays

int[][] tab = new int[8][3]; // 8 rows, 3 columns

int[][] c = { {5, 8}, {1, 2, 9}, {7, 4, 2} };

// What is c[1][2] ?

// What is c.length ?

Arrays, quick remainder (2 / 2)

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Arrays are objects!

But of what class..?

This is implicit (“hidden” to a programmer).E.g. the name of a 1-dim array of int’s is [I,

the name of a 2-dim array of int’s is [[I,the name of a 1-dim array of double’s is [D etc.

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Coping with array copying

int[] a; int[] b = {5, 6, 7, 8, 9};a = b; // WRONG ! Copied a reference, not the 5 elements of b

Correct:a = new int[b.length];for(int i=0; i < b.length; i++) a[i] = b[i];

There is a copy method in java.lang.System: arraycopy(sourceArr, src_pos, destArr, dest_pos, length);

Example: System.arraycopy(b, 0, a, 0, b.length);

Exceptions possible: NullPointerException (if sourceArray or destArray null), IndexOutOfBoundsException (e.g. src_pos negative), or ArrayStoreException

(element type mismatch).

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arraycopy demo[ http://java.sun.com/docs/books/tutorial/java/nutsandbolts/arrays.html ]

Output:caffein

int[] a = {1, 2, 3};int[] b = a; b[0] = 10; // a[0] also changed, of course

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Up to v1.4, this was a feature from C/C++ missing in Java.Same notation used (ellipsis).

Argument list: type ... identifier.The type can be anything, even an array.

Each method can only have a single type as a variable argument and it must come last in the parameter list.

Variable length argument lists (since SDK 5.0)

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Varargs, example(based on [W. Clay Richardson et al., Professional Java,

JDK 5 Edition, Wrox, 2005])

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Previous example,can we have int sum(int[]) signatureand still use e.g. sum(5, 10, -30)?

Answer: no, the compiler reports an error. You can use sum(new int[] {5, 10, -30}) instead.

Actually, the ellipsis is just syntactic sugar for having the compiler create and initialize an array of same-typed values and pass that array’s reference to a method.

http://today.java.net/pub/a/today/2004/04/19/varargs.html

When the ellipsis can be used?E.g., for computing the average of a list (of e.g. floats),

concatenating a list of strings into a single string, finding the max/min values in lists of floats.

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Varargs, example with arrays(based on [W. Clay Richardson et al., Professional Java,

JDK 5 Edition, Wrox, 2005])

Varargs, if at least one argument required(J.Bloch’s presentation, S48–49,

http://files.meetup.com/1381525/still-effective.ppt.pdf)

No args – fails at runtime.

OK!No args –

compile error.

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Other constructs (mostly) from C/C++

Loops:

for(exp1; exp2; exp3) …

for(T x: array_of_type_T) … // for-each

while (expr) instr;

do (inst) while (expr);

Selection:

switch (expr) { case var1: inst1; case var2: instr2; ... default: instr_def;}

Java 7

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Switch specifics

The variable used in a switch statement can be an integer value of up to 32 bits,

i.e.: byte, short, int, or char,or a wrapper class (Byte etc.) (*),

or an enum (*).

Or a string (since Java 7).(*) discussed later

The value for a case must be the same data type as the variable in the switch, and it must be a

constant or a literal.

You cannot list more than one value after a single case.

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Not quite C/C++ constructs

break and continue made more flexible.

int i = 0, j = 0;outerloop: // labelwhile (i < 100){ i++; while (true) { j++; if (i + j > 10) break outerloop; // escapes to (*) }} // (*)

A reasonable compromise betweenstiff break / continue

in C/C++and most flexible but

messy goto(in many languages).

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What is b:double b = 1 / 3; // ?

Just like in C/C++: integer division, result: 0.To obtain 0.3333333... use 1.0 / 3.0.

Data conversion

And now, what is c?int c = 1.0 / 3.0;

Compile error.Java wants to make sure you know

you’d lose fractional information.

Solution: int c = (int)(1.0 / 3.0);

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Type conversions (arithmetic)

int i;

short sh;

sh = 5; // OK; 5 is int but is constant and // is small enough (no information loss)

i = sh; // expanding, ok

sh = (short)i; // OK – with the explicit cast

int2int

double d = 5.12;

i = d; // WRONG! Conversion must be explicit

// but:i = (int)d; // OK. The fraction is cut off

float2int

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Integer arithmetic

Java performs integer arithmetic at the int level, so e.g. b+c, where b and c are of type short, returns an int.

The sum must therefore be cast to a short before an assignment to a, because a is a short:

short a, b, c;c = 21; b = 9;a = (short) (b + c); // without casting – a compile error

Similar example:

byte a=4, b=-1; short c = (short)(a+b);

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What’s wrong with that?

float width = 5.5; // compile error

Compiler message:possible loss of precisionfound: doublerequired: float

So, you should’ve written float width = (float)5.5; // explicit cast

or (more naturally)float width = 5.5F; // or ...5.5f

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Long division [ J. Bloch, N. Gafter, Java Puzzlers ]

Output: 5

Correction: ... = 24L * ...(only in MICROS_PER_DAY is enough)

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Very much like in C/C++.Returned type declaration (possibly void), name,

parameters... return keyword.

Passing variables in Java always by value – a copy is made.

No change of the variable in the called method affectsits value when back in the caller.

Aren’t some variables passed by reference though??No. The reference’s (memory location’s) copy

is passed to the second method.This works for objects (incl. arrays).

Methods (functions)

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References

Declaring an object is in fact only declaring a reference to it(no memory allocation for the object itself).

This is different than with simple types (e.g. int)!

Button b; // declaring a reference to a Button object

b = new Button(); // now we create the object

(Kind of) a special case: String objects.String s = "George Bush"; // !!

What about String s = new String("George Bush"); // ??

It’s correct too, but it’s beating around the bush.

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Little trap?

String s1 = "abc"; String s2 = "ab";

s2 += "c";boolean result = (s1 == s2); // true?

False. Different objects (i.e., their references point to different memory locations). Content irrelevant.

How to compare content then?if (s1.equals(s2)) ... or

if (s1.equalsIgnoreCase(s2)) ...

String s1 = "abc"; String s2; s2 = s1; // copy?

No, just another reference. Write s2 = new String(s1); if a copy needed.

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Concatenating strings and numbers

String s1 = "Johnny has drunk ";int count1 = 2, count2 = 1;

String s2 = " beers.";String s3 = s1 + count1 + s2;

String s4 = s1 + (count1 + count2) + s2; String s5 = s1 + count1 + count2 + s2;

String s6 = count1 + count2 + s2;

What do s3, s4, s5, s6 store?

Remember: evaluation from left to right.

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Time for a little something [ http://www.javalobby.org/eps/more-puzzlers/ ]

Answer: d. (Prints just “false”.)Because the + operator binds tighter than ==.

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Obvious fix

But wait. pig and dog are both final. Can’t we use the == operator then? With "Animals... " + (pig == dog) expression?

No. That's because evaluation of dog needs invokinga method (length(), for the object pig, in our case)

which must be done in the runtime.Hence, pig and dog are physically separate strings.

But note: final String pig = "length: 10"; final String dog = "length: 10";

// here pig == dog !

String literals are “interned” by the JVM

s1 equals s2 ? trues1 == s2 ? falses2 == s3 ? truefs1 == fs2 ? true

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More on strings

Lots of functionality in String class. See:http://java.sun.com/j2se/1.4.2/docs/api/java/lang/String.html

A few examples:

String c = "Abcde ".substring(2,4);if (c.startsWith("b")) System.err.println("What the hell?!");c += " ";String d = c.trim(); // leading and trailing whitespace removedfloat f = 5.001f;String s = d.valueOf(f); // s.equals("5.001")==true now// valueOf is a static method from class String// object name here (d) irrelevant – String.valueOf(f) means the samec = c.toUpperCase(); // what if we write just: c.toUpperCase(); ?System.out.println(c.length());

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More on strings

String s = "Abcde ".substring(2,8); /* Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 8 */

Maybe you meantString s = "Abcde ".substring(2, Math.min(8, "Abcde ".length()));

String s = "abracadabra";system.out.print(s.lastIndexOf("ab")); // 7system.out.print(s.lastIndexOf("abb")); // -1, not found

4242

String vs StringBuffer (1/3)

Objects of class String are immutable in Java.

String s = "test";s[0] = 'b'; // compile-error:// array required, but java.lang.String found

There is charAt(int i) method in String, but only to read.

So, how can we e.g. append a character to a String?!Short answer: we cannot.

We need to create another String:String s1 = "ice-cream";

s1 = s1 + "s"; // SLOW esp. if s1 is long// creates a temp object

4343

String vs StringBuffer (2/3)[ http://java.sun.com/javase/6/docs/api/java/lang/StringBuffer.html ]

Class StringBuffer – smth like String but its objectscan be modified.

At any point in time it contains some particular sequence of chars, but its length and content can be changed through certain method calls.

StringBuffer sb = new StringBuffer(new String("start"));

sb.append("le"); // "startle"or:

sb.insert(4, "le"); // start starlet

4444

String vs StringBuffer (3/3)[ http://java.sun.com/javase/6/docs/api/java/lang/StringBuffer.html ]

[ http://mindprod.com/jgloss/immutable.html ]

Every string buffer has a capacity.Initially (JDK 6) – 16 characters for an empty

string buffer, and 16 + |str| if usingpublic StringBuffer(String str) constructor.

If the internal buffer overflows, it is automatically made larger.

Why String immutable?• thread-safe. Two threads can both work on an immutable object

at the same time without any possibility of conflict;• immutable objects are much better suited to be

Hashtable/HashMap etc. keys. If you change the value of an object that is used as a hash table key without removing it and re-adding it, you lose the mapping.

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Scanner classBreaks its input into tokens using a delimiter pattern (by default:

whitespace). Convenient nextXxxx() methods for type conversion.

Examples:Scanner sc1 = new Scanner(new File("myNumbers"));while (sc1.hasNextLong())

long aLong = sc1.nextLong();

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Scanner, various inputs are possible[ http://java.sun.com/j2se/1.5.0/docs/api/java/util/Scanner.html ]

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Math class

http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Math.html

sin, cos, tan, atan, asin, ...exp, log (base e), ceil, floor, sqrt, ...

min, max (lesser or greater of a pair),pow(a, b), random() (from [0,1))

static double toDegrees(double angrad),static double toRadians(double angdeg)

rint(double a) – returns the double value that is closest in value to arg. a and is equal to a mathematical

integer. Rounding to an even, in case of a “tie”.

Constants: PI, E

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javadoc (1)

Writing documentation to large software projects:both very tedious and very important.

javadoc is a simple tool to fascilitate it.Just comment each (public) function in the classes

and run javadoc – the whole documentation will be generated (as a set of html pages).

Sun Microsystem’s on-line documentation for the standard Java API was produced using javadoc.

The documentation for each item must be placed in a comment that precedes the item. (This is how javadoc

knows which item the comment is for.)

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javadoc (2)

Javadoc documentation in /** ... */.Special notation allowed:

@return, @param.

/** * Return the real number represented by the string s, * or return Double. NaN if s does not represent a legal * real number. * * @param s String to interpret as real number. * @return the real number represented by s. */

public static double stringToReal(String s) { try { return Double.parseDouble(s); } catch (NumberFormatException e) { return Double.NaN; } }

Fromhttp://www.faqs.org/docs/javap/advanced.html

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Classes

Class is an object type. Basic syntax similar to C++.

class WackyWindow{... // data & methods WackyWindow(int x, int y) // constructor { ... } } // no ; as opposed to C++

In Java, method bodies are inside the class.

Object-oriented programming is an exceptionally bad idea

which could only have originated in California.

/ Edsger Dijkstra /

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Constructor (example based on [Barteczko’00])

class Pair{

int a, b;Pair(int x, int y){

a=x;b=y;

}void add(Pair p){

a+=p.a;b+=p.b;

}}

class Pair{

int a, b;Pair(int x) // single param.{

a=x;b=x;

}}

52

Default (=no-arg) constructor

class X { int i, j; void setState(int a, int b) { i = a; j = b; } void showState() { ... }}...X x = new X(); // OK (default constructor launched)

But if we hadclass X { ... X(int a, int b) { ... } // "standard" constructor}thenX x = new X(); // compile error

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Keyword this (only in methods)

Pair add(Pair p) { a = a + p.a; b = b + p.b; return this;}...p.add(p1);p.add(p2);p.add(p3);

But you can also typep.add(p1).add(p2).add(p3); // !

Why?

this – reference to the current object

54

this in a constructor

class Date {int year, month, day;public Date(int d, int m, int y) // one constructor{

day = d; month = m; year = y; }

public Date(int y) { this(1, 1, y); } // anotherpublic Date( ) // yet another constructor {

this(2008); }

} Based on an example fromhttp://www.cs.fiu.edu/~weiss/cop3338_f00/lectures/Objects/objects.pdf

55

this specifics

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Hiding identifiers

You can’t do it in blocks:int a;{ int a; // COMPILE ERROR}

Class fields can be hidden:class A { int a; void method(){ int a = 0; // local var. a = a + 10; // local var. this.a++; // field of the object } ...

This is wrong too:int i = 0;for (int i = 0; i < 10; i++) { ... }

57

Method overloading

• int Fun(int x)• int Fun(float y)• int Fun(int a, float b)

All they can appear in one class.

But not• int Fun(int x)

and• boolean Fun(int y)

58

PackagesPackages are class libraries.

To include (“import”) a package in your code,write smth like import java.util.*;

Or you want to import a single class for a package?Example: import java.util.ArrayList;

java.lang package is automatically imported.

Using an imported class: either (in the same example) java.util.ArrayList or just ArrayList.

More convenient than in C/C++: you can import a package more than once (no compiler complaint...),

you can write the import... line in any place in your code.

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Packages, cont’d

Collisions possible:Say that you’ve created a class Vector in a package

called school.my_cool_data_structures.

But you’ve also imported java.util.

Now, the line Vector v = new Vector();makes a collision.

Solution: use full path.java.util.Vector v = new java.util.Vector();

orschool.my_cool_data_structures.Vector v =

new school.my_cool_data_structures.Vector()

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How to create an own package

Very simply.

Just write the code of your class (in a file with the same name as the class name)and start it with line e.g.

package myutils.text;Your class will be added to the package myutils.text.

Of course, there can be many classes in a package.Remember: earlier in the file than the package... line

may be only comments.

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Access modifiers (for classes, methods, fields)[ http://www.particle.kth.se/~lindsey/JavaCourse/Book/

Part1/Java/Chapter05/access.html ]

Java provides 4 access modifiers:

1.public – access by any other class anywhere.

2.protected – accessible by the package classes and any subclasses that are in other packages.

3. default (also known as “package private”) – accessible to classes in the same package but not by classes in other packages, even if these are subclasses.

4.private – accessible only within the class. Even methods in subclasses in the same package do not have access.A Java file can have only one public class!

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Access modifiers, visualized [ members.tripod.com/~psdin/comlang/basicJava.PDF ]

If there is no direct access to a field (property),provide accessor / mutator (aka get / set) methods.

no!

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Why private (or protected)?

To avoid accidental “spoiling” of some data.

To provide a proper class interface(ensapsulation rule: hide unimportant details).

C++ programmers, beware:put public / protected / private in front of

EACH method or field you want to specify that way.(In C++, in contrast, an access specifier is valid for all

the definitions following it until another access specifier occurs.)

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Default packageclass X { // file X.java int x; void doSomething() { ... }}

class Y { // file Y.java in the same directory void someMethod() { X x = new X(); x.doSomething(); // does it work? Can Y see components of X ? }} X’s components are NOT public.

So the question is: are Y and X in the same package?

We didn’t write package ...

Yes!

Because they are in the same directory and have no explicit package name.

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Fields are initialized to ZERO (0, false for the boolean type, null for references (i.e., object types)).

BEWARE: local variables are not initialized (have random values)! Like in C/C++, by the way.

But trying to read an unitialized variable yields a compile error.

Field initialization

You can also explicitly initialize a field, e.g.

class Pair { static String text = "Pairs"; static int x = -1; int a = x+1; .....

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Field initialization, cont’d

We can also init object fields, e.g.class X { Flower f = new Flower(); ...}

Or like that:class X { int i = f(); int j = g(i); .....}

But not .....

int j = g(i); int i = f(); // order matters!

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More on cleanup

Two ways: finalization and garbage collection.

From Eckel’s TIJ, 3rd ed., chapter 4:Java provides a method called finalize() that you can

define for your class. Here’s how it’s supposed to work. When the garbage collector is ready to release the

storage used for your object, it will first call finalize(), and only on the next garbage-collection pass will it

reclaim the object’s memory. So if you choose to use finalize(), it gives you the ability to perform some

important cleanup at the time of garbage collection.

But what for can we need finalize()?

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Trap for C++ programmers

GC or finalize() method are NOT equivalent to destroying an object (with the class destructor) in C++!

The reason is, in C++ objects always get destroyed(and the programmer controls this moment)

while in Java – not. (Perhaps an object will be destroyed, i.e. its storage will be garbage-collected (when? We don’t know),

or perhaps not... – to save time.)

1. Your objects might not get garbage collected.2. Garbage collection is not destruction.[ B.Eckel, Thinking in Java, 3rd ed., chapter 4 ]

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So, what do we need finalize() for??

We may allocate space using native methods,i.e. calling non-Java code from Java.

Example: allocate memory with C’s malloc().Until free() called, storage will not be released.

Of course, free() is a C and C++ function, so we need to call it in a native method inside our finalize().

But I won’t use that ugly C or C++ in my Java code!So, I will never need finalize(), right?

Not quite true...

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finalize(), interesting use[ B.Eckel, Thinking in Java ]

Verification of the termination condition of an object.

When we’re no longer interested in an object, itshould be in a state whereby its memory can be

safely released. E.g. the object is an open file, that file should be

explicitly closed before the object is garbage collected.

The value of finalize() is that it can be used to eventually discover this condition, even if it isn’t always called. If

one of the finalizations happens to reveal the bug, then you discover the problem.

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finalize(), interesting use, cont’dCode example (1/2) [ B.Eckel, Thinking in Java ]

72

finalize(), interesting use, cont’dCode example (2/2) [ B.Eckel, Thinking in Java ]

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Static data, static methods

static int n; // the field n belongs not to an individual object // but to the class// all class objects “see” the same value of n

Static method – belongs to the class. It can access only static fields of the class. this not accessible.

A static method cannot access non-static fields.Why? Since perhaps no object yet exists when

we launch this method.(But a non-static method can invoke a static method,

or access a static field.)

74

We already used API static methods

System.out.println(Math.sqrt(2)); /* OK, although no Math object created */

Can we also do it like that?Math m = new Math();System.out.println(m.sqrt(2));

No. The Math constructor isprivate.

75

String Tokenizer – useful class

import java.util.*; ...String speech = "A lion, a witch...";StringTokenizer st = new StringTokenizer(speech);while (st.hasMoreTokens()) { System.out.println(st.nextToken());}

Prints:

A lion, a witch...

Comments: 1-param constructor, hencedefault separators (spaces, CR, tabs).

Wanna have .,: and space separators? Type...new StringTokenizer(speech, ".,: ");

Alternatives: Scanner, String.split.