ComputerScienceReference-StatementControl

8/9/2019 ComputerScienceReference-StatementControl

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4. Statement Control

4. 1. Statement( 8 ) 4. 8. Break Statement( 5 )

4. 2. If Statement( 9 ) 4. 9. Continue Statement( 4 )

4. 3. Switch Statement( 6 ) 4. 10. try catch( 6 )

4. 4. While Loop( 4 ) 4. 11. throw( 2 )4. 5. Do While Loop( 2 ) 4. 12. finally( 1 )

4. 6. For Loop( 14 ) 4. 13. throws signature( 1 )

4. 7. For Each Loop( 8 )

4. 1. Statement4. 1. 1. An Overview of Java Statements

4. 1. 2. Expressions

4. 1. 3. Declaring and defining multiple variables in a single statement4. 1. 4. Label a statement block

4. 1. 5. Spreading a single declaration over several lines4. 1. 6. How to write multiple assignments in a single statement4. 1. 7. Combining both statements into one

4. 1. 8. Statement Blocks

4. 1. 1. An Overview of Java StatementsIn programming, a statement is an instruction to do something.

It controls the sequence of execution of a program.

In Java, a statement is terminated with a semicolon and multiple statements can be written on a single line.

x = y + 1; z = y + 2;In Java, an empty statement is legal and does nothing: ;

4. 1. 2. ExpressionsSome expressions can be made statements by terminating them with a semicolon. For example, x++ is an

expression. However, this is a statement:

x++;

Statements can be grouped in a block. A block is a sequence of the following programming elements within braces:

statements

local class declarationslocal variable declaration statements

4. 1. 3. Declaring and defining multiple variables in a single statementA comma separates each variable.

public class MainClass

{public static void main(String[] arg)

{

long a = 999999999L, b = 100000000L;int c = 0, d = 0;


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System.out.println(a);System.out.println(b);

System.out.println(c);

System.out.println(d);

}

}4. 1. 4. Label a statement blockA statement and a statement block can be labeled.

Label names follow the same rule as Java identifiers and are terminated with a colon.

public class MainClass{

public static void main(String[] args)

{

int x = 0, y = 0;sectionA: x = y + 1;

}

}And, here is an example of labeling a block:



{

start:{

// statements

}}

}Label statement can be referenced by the break and continue statements.

4. 1. 5. Spreading a single declaration over several linespublic class MainClass{

public static void main(String[] arg)

{int a = 0, // comment for a

b = 0, // comment for b

c = 0, // comment for cd = 0;

System.out.println(a);System.out.println(b);

System.out.println(c);

System.out.println(d);}

}


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4. 1. 6. How to write multiple assignments in a single statementpublic class MainClass

{

public static void main(String[] argv){

int a, b, c;a = b = c = 777;

System.out.println(a);

System.out.println(b);

System.out.println(c);}

}

Output:777

777

777

4. 1. 7. Combining both statements into oneclass Animal {

public Animal(String aType) {type = aType;

}

public String toString() {return "This is a " + type;

}

private String type;

}public class MainClass {

public static void main(String[] a) {

System.out.println(new Animal("a").getClass().getName()); // Output the// class name

}

}Output:

Animal

4. 1. 8. Statement Blocks

You can have a block of statements enclosed between braces.If the value of expression is true, all the statements enclosed in the block will be executed.

Without the braces, the code no longer has a statement block.


public static void main(String[] arg)

{int a = 0;

if (a == 0)


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{

System.out.println("in the block");System.out.println("in the block");

}

}

}

Output:in the block

in the block

4. 2. If Statement

4. 2. 1. The if statement syntax

4. 2. 2. Expression indentation for if statement4. 2. 3. Using braces makes your 'if' statement clearer

4. 2. 4. Multiple selections4. 2. 5. The if Statement in action4. 2. 6. The else Clause

4. 2. 7. Nested if Statements

4. 2. 8. Using && in if statement

4. 2. 9. Using || (or operator) in if statement

4. 2. 1. The if statement syntaxThe if statement is a conditional branch statement. The syntax of the if statement is either one of these two:

if (booleanExpression){

statement (s)}

or

if (booleanExpression)

{statement (s)

}

else{

statement (s)}

For example, in the following if statement, the if block will be executed if x is greater than 4.



{int x = 9;

if (x > 4)


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{

// statements}

}

}

In the following example, the if block will be executed if a is greater than 3. Otherwise, the else block will be executed.

public class MainClass

{

public static void main(String[] args){

int a = 3;

if (a > 3)

{// statements

}

else{

// statements

}}

}

4. 2. 2. Expression indentation for if statementIf the expression is too long, you can use two units of indentation for subsequent lines.


public static void main(String[] args){

int numberOfLoginAttempts = 10;

int numberOfMinimumLoginAttempts = 12;

int numberOfMaximumLoginAttempts = 13;int y = 3;

if (numberOfLoginAttempts < numberOfMaximumLoginAttempts ||

numberOfMinimumLoginAttempts > y)

{y++;

}

}}

4. 2. 3. Using braces makes your 'if' statement clearerIf there is only one statement in an if or else block, the braces are optional.

public class MainClass {

public static void main(String[] args) {


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int a = 3;

if (a > 3)a++;

else

a = 3;

}

}

Consider the following example:



int a = 3, b = 1;

if (a > 0 || b < 5)

if (a > 2)

System.out.println("a > 2");

elseSystem.out.println("a < 2");

}

}

It is hard to tell which if statement the else statement is associated with.

Actually, An else statement is always associated with the immediately preceding if.

Using braces makes your code clearer.



int a = 3, b = 1;

if (a > 0 || b < 5) {

if (a > 2) {

System.out.println("a > 2");} else {

System.out.println("a < 2");

}}

}

}

4. 2. 4. Multiple selectionsIf there are multiple selections, you can also use if with a series of else statements.

if (booleanExpression1) {// statements


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} else if (booleanExpression2) {

// statements}

...

else {

// statements

}For example:


public static void main(String[] args) {int a = 0;

if (a == 1) {System.out.println("one");

} else if (a == 2) {

System.out.println("two");

} else if (a == 3) {System.out.println("three");

} else {

System.out.println("invalid");}

}

}

4. 2. 5. The if Statement in actionpublic class MainClass {

public static void main(String[] arg) {int a = 0;

if (a == 0) {System.out.println("a is 0");

}

}}

a is 0

4. 2. 6. The else Clausepublic class MainClass {

public static void main(String[] arg) {

int a = 0;

if (a == 0) {


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System.out.println("in the block");

System.out.println("in the block");} else {

System.out.println("a is not 0");

}

}

}in the block

in the block

4. 2. 7. Nested if Statementspublic class MainClass {

public static void main(String[] arg) {int a = 2;

if (a == 0) {

System.out.println("in the block");if (a == 2) {System.out.println("a is 0");

} else {

System.out.println("a is not 2");}

} else {System.out.println("a is not 0");

}

}

}a is not 0

4. 2. 8. Using && in if statementpublic class MainClass {


int value = 8;

int count = 10;int limit = 11;

if (++value % 2 == 0 && ++count < limit) {System.out.println("here");

System.out.println(value);

System.out.println(count);

}System.out.println("there");

System.out.println(value);

System.out.println(count);


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}

}there

9

10

4. 2. 9. Using || (or operator) in if statementpublic class MainClass {


int value = 8;int count = 10;

int limit = 11;

if (++value % 2 != 0 || ++count < limit) {

System.out.println("here");

System.out.println(value);System.out.println(count);}

System.out.println("there");

System.out.println(value);System.out.println(count);

}

}here

9

10

there9

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4. 3. Switch Statement

4. 3. 1. The switch Statement4. 3. 2. The switch Statement: a demo

4. 3. 3. Execute the same statements for several different case labels

4. 3. 4. Free Flowing Switch Statement Example4. 3. 5. Nested Switch Statements Example

4. 3. 6. Switch statement with enum

4. 3. 1. The switch StatementAn alternative to a series of else if is the switch statement.

The switch statement allows you to choose a block of statements to run from a selection of code, based

on the return value of an expression.The expression used in the switch statement must return an int or an enumerated value.

The syntax of the switch statement is as follows.

switch (expression) {


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case value_1 :

statement (s);

break;

case value_2 :

statement (s);

break;.

.

.

case value_n :

statement (s);break;

default:

statement (s);}

Failure to add a break statement after a case will not generate a compile error but may have more

serious consequences because the statements on the next case will be executed.

Here is an example of the switch statement:



int i = 1;switch (i) {

case 1 :

System.out.println("One.");

break;case 2 :

System.out.println("Two.");

break;case 3 :

System.out.println("Three.");

break;default:

System.out.println("You did not enter a valid value.");

}}

}

4. 3. 2. The switch Statement: a demo


public static void main(String[] args) {int choice = 2;

switch (choice) {case 1:


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System.out.println("Choice 1 selected");

break;case 2:

System.out.println("Choice 2 selected");

break;

case 3:

System.out.println("Choice 3 selected");break;

default:System.out.println("Default");

break;

}}

}

Choice 2 selected

4. 3. 3. Execute the same statements for several different case labels



char yesNo = 'N';

switch(yesNo) {

case 'n': case 'N':System.out.println("No selected");

break;

case 'y': case 'Y':

System.out.println("Yes selected");break;

}

}}

No selected

4. 3. 4. Free Flowing Switch Statement Example

public class Main {


int i = 0;

switch (i) {

case 0:

System.out.println("i is 0");

case 1:System.out.println("i is 1");

case 2:

System.out.println("i is 2");default:


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System.out.println("Free flowing switch example!");

}}

}

/*

i is 0

i is 1i is 2

Free flowing switch example!*/

4. 3. 5. Nested Switch Statements Examplepublic class Main {

public static void main(String[] args) {int i = 0;

switch (i) {

case 0:

int j = 1;switch (j) {

case 0:

System.out.println("i is 0, j is 0");break;

case 1:

System.out.println("i is 0, j is 1");break;

default:

System.out.println("nested default case!!");

}break;

default:

System.out.println("No matching case found!!");}

}

}//i is 0, j is 1

4. 3. 6. Switch statement with enumpublic class MainClass {

enum Choice { Choice1, Choice2, Choice3 }


Choice ch = Choice.Choice1;

switch(ch) {

case Choice1:System.out.println("Choice1 selected");

break;



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break;


break;

}

}

}Choice1 selected

4. 4. While Loop

4. 4. 1. The while Statement

4. 4. 2. Using the while loop to calculate sum4. 4. 3. While loop with double value

4. 4. 4. Java's 'labeled while' loop

4. 4. 1. The while Statement

One way to create a loop is by using the while statement.

Another way is to use the for statementThe while statement has the following syntax.

while (booleanExpression) {

statement (s)}

statement(s) will be executed as long as booleanExpression evaluates to true.

If there is only a single statement inside the braces, you may omit the braces.For clarity, you should always use braces even when there is only one statement.

As an example of the while statement, the following code prints integer numbers that are less than

three.



int i = 0;

while (i < 3) {

System.out.println(i);i++;

}

}

}

To produce three beeps with an interval of 500 milliseconds, use this code:


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int j = 0;

while (j < 3) {

java.awt.Toolkit.getDefaultToolkit().beep();

try {Thread.currentThread().sleep(500);

} catch (Exception e) {}

j++;

}}

}Sometimes, you use an expression that always evaluates to true (such as the boolean literal true) but

relies on the break statement to escape from the loop.



int k = 0;while (true) {

System.out.println(k);

k++;if (k > 2) {

break;

}

}}

}

4. 4. 2. Using the while loop to calculate sumpublic class MainClass {


int limit = 20;int sum = 0;

int i = 1;

while (i


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4. 4. 3. While loop with double valuepublic class MainClass {


double r = 0;

while(r < 0.99d) {

r = Math.random();System.out.println(r);

}}

}

0.43772789973053870.2688654455422754

0.36392537297385574

0.152544135113610420.6688621030424611

0.143156733550304

0.3867695752401421

0.63484960311260750.8262243996358971

0.057290108917235516

4. 4. 4. Java's 'labeled while' loop


public static void main(String[] args) {int i = 0;

outer: while (true) {

System.out.println("Outer while loop");

while (true) {i++;

System.out.println("i = " + i);

if (i == 1) {System.out.println("continue");

continue;

}if (i == 3) {

System.out.println("continue outer");

continue outer;}

if (i == 5) {

System.out.println("break");

break;}

if (i == 7) {

System.out.println("break outer");break outer;

}

}}


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}

}Outer while loop

i = 1

continue

i = 2

i = 3continue outer

Outer while loopi = 4

i = 5

breakOuter while loop

i = 6

i = 7break outer

4. 5. Do While Loop4. 5. 1. The do-while Statement

4. 5. 2. The do while loop in action

4. 5. 1. The do-while Statement

The do-while statement is like the while statement, except that the associated block always gets

executed at least once.

Its syntax is as follows:

do {statement (s)

} while (booleanExpression);

Just like the while statement, you can omit the braces if there is only one statement within them.However, always use braces for the sake of clarity.



int i = 0;

do {System.out.println(i);

i++;

} while (i < 3);}

}This prints the following to the console:


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01

2

The following do-while demonstrates that at least the code in the do block will be executed once even

though the initial value of j used to test the expression j < 3 evaluates to false.



int j = 4;

do {System.out.println(j);

j++;

} while (j < 3);}

}

This prints the following on the console.

4

4. 5. 2. The do while loop in action

do {

// statements} while (expression);




int i = 1;

do {

sum += i;

i++;} while (i


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4. 6. 2. For statement in detail

4. 6. 3. A loop allows you to execute a statement or block of statements repeatedly4. 6. 4. The numerical for loop

4. 6. 5. Infinite For loop Example

4. 6. 6. initialization_expression: define two variables in for loop

4. 6. 7. Declare multiple variables in for loop

4. 6. 8. Multiple expressions in for loops4. 6. 9. To omit any or all of the elements in 'for' loop: but you must include the semicolons

4. 6. 10. Keeping the middle element only in for loop4. 6. 11. Using the Floating-Point Values as the control value in a for loop

4. 6. 12. Nested for Loop

4. 6. 13. Java's 'labeled for' loop4. 6. 14. Print out a Diamond

4. 6. 1. The for Statement

The for statement is like the while statement, i.e. you use it to create loop. The for statement has

following syntax:

for ( init ; booleanExpression ; update ) {

statement (s)

}init is an initialization that will be performed before the first iteration.

booleanExpression is a boolean expression which will cause the execution of statement(s) if it

evaluates to true.update is a statement that will be executed after the execution of the statement block.

init, expression, and update are optional.

The for statement will stop only if one of the following conditions is met:

booleanExpression evaluates to false

A break or continue statement is executed

A runtime error occurs.

4. 6. 2. For statement in detailIt is common to declare a variable and assign a value to it in the initialization part. The variable

declared will be visible to the expression and update parts as well as to the statement block.

For example, the following for statement loops five times and each time prints the value of i. Note that

the variable i is not visible anywhere else since it is declared within the for loop.



for (int i = 0; i < 5; i++) {System.out.println(i + " ");

}

}}


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The initialization part of the for statement is optional.



int j = 0;

for (; j < 3; j++) {System.out.println(j);

}// j is visible here

}

}

The update statement is optional.



int k = 0;for (; k < 3;) {

System.out.println(k);

k++;}

}

}

You can even omit the booleanExpression part.



int m = 0;for (;;) {

System.out.println(m);

m++;if (m > 4) {

break;

}}

}

}If you compare for and while, you'll see that you can always replace the while statement with for. This

is to say that

while (expression) {

...

}


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can always be written as

for ( ; expression; ) {

...

}

4. 6. 3. A loop allows you to execute a statement or block of statements repeatedlypublic class MainClass {


for (int i = 0; i < 8; i++) {System.out.println("Hi.");

}

}}

Hi.

Hi.

Hi.Hi.

Hi.

Hi.Hi.

Hi.

4. 6. 4. The numerical for loop

for (initialization_expression ; loop_condition ; increment_expression) {

// statements}


public static void main(String[] args) {int limit = 20; // Sum from 1 to this value

int sum = 0; // Accumulate sum in this variable

for (int i = 1; i


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System.out.println("Hello");

break;}

}

}

//Hello

4. 6. 6. initialization_expression: define two variables in for looppublic class MainClass {

public static void main(String[] arg) {int limit = 10;

int sum = 0;

for (int i = 1, j = 0; i


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i = 2 j= -2

i = 3 j= -3i = 4 j= -4

*/

4. 6. 9. To omit any or all of the elements in 'for' loop: but you must include the semicolonspublic class MainClass {


int limit = 10;

int sum = 0;

for (int i = 1; i


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radius = 1.0area = 3.141592653589793

radius = 1.2area = 4.523893421169302radius = 1.4area = 6.157521601035994

radius = 1.5999999999999999area = 8.04247719318987

radius = 1.7999999999999998area = 10.178760197630927

radius = 1.9999999999999998area = 12.566370614359169

4. 6. 12. Nested for Looppublic class MainClass {


long limit = 20L;long factorial = 1L;

for (long i = 1L; i


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inner: for (; i < 10; i++) {

System.out.println("i = " + i);if (i == 2) {

System.out.println("continue");

continue;

}

if (i == 3) {System.out.println("break");

i++;break;

}

if (i == 7) {System.out.println("continue outer");

i++;

continue outer;}

if (i == 8) {

System.out.println("break outer");

break outer;}

for (int k = 0; k < 5; k++) {

if (k == 3) {System.out.println("continue inner");

continue inner;

}}

}

}

}}

i = 0

continue inneri = 1

continue inner

i = 2continue

i = 3

breaki = 4

continue inner

i = 5

continue inneri = 6

continue inner

i = 7continue outer

i = 8

break outer


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4. 6. 14. Print out a Diamondclass Diamond {


for (int i = 1; i < 10; i += 2) {

for (int j = 0; j < 9 - i / 2; j++)

System.out.print(" ");

for (int j = 0; j < i; j++)System.out.print("*");

System.out.print("\n");}

for (int i = 7; i > 0; i -= 2) {for (int j = 0; j < 9 - i / 2; j++)

System.out.print(" ");

for (int j = 0; j < i; j++)System.out.print("*");

System.out.print("\n");}

}

}/*

*

***

************

*********

************

***

**/

4. 7. For Each Loop

4. 7. 1. The For-Each Version of the for Loop

4. 7. 2. The for-each loop is essentially read-only

4. 7. 3. The for each loop for an enum data type4. 7. 4. Using the For-Each Loop with Collections: ArrayList

4. 7. 5. Use a for-each style for loop

4. 7. 6. Using 'for each' to loop through array4. 7. 7. Iterating over Multidimensional Arrays: Use for-each style for on a two-dimensional

array

4. 7. 8. Using break with a for-each-style for


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4. 7. 1. The For-Each Version of the for Loop

The general form of the for-each version of the for is shown here:

for(type itr-var : iterableObj) statement-block

The object referred to by iterableObj must be an array or an object that implements the new Iterable

interface.

4. 7. 2. The for-each loop is essentially read-only

public class MainClass {public static void main(String args[]) {

int nums[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

for(int x : nums) {

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

x = x * 10; // no effect on nums}

System.out.println();

for(int x : nums)

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

System.out.println();

}

}1 2 3 4 5 6 7 8 9 10

1 2 3 4 5 6 7 8 9 10

4. 7. 3. The for each loop for an enum data typefor (type identifier : iterable_expression) {

// statements

}public class MainClass {

enum Season {

spring, summer, fall, winter}

public static void main(String[] args) {for (Season season : Season.values()) {

System.out.println(" The season is now " + season);

}

}}

The season is now spring

The season is now summerThe season is now fall

The season is now winter

4. 7. 4. Using the For-Each Loop with Collections: ArrayList


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For-Each Loop can be used to any object that implements the Iterable interface. This includes all

collections defined by the Collections Framework,

import java.util.ArrayList;


public static void main(String args[]) {

ArrayList list = new ArrayList();

list.add(10.14);

list.add(20.22);list.add(30.78);

list.add(40.46);

double sum = 0.0;

for(double itr : list)

sum = sum + itr;

System.out.println(sum);

}

}101.6

4. 7. 5. Use a for-each style for looppublic class MainClass {


int nums[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

int sum = 0;

// use for-each style for to display and sum the values

for(int x : nums) {System.out.println("Value is: " + x);

sum += x;

}

System.out.println("Summation: " + sum);

}}

Value is: 1

Value is: 2

Value is: 3Value is: 4

Value is: 5


Value is: 8



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Summation: 55

4. 7. 6. Using 'for each' to loop through array



char[] vowels = { 'a', 'e', 'i', 'o', 'u'};

for(char ch: vowels){System.out.println(ch);

}

}}

a

ei

o

u

4. 7. 7. Iterating over Multidimensional Arrays: Use for-each style for on a two-dimensional array

public class MainClass {public static void main(String args[]) {

int sum = 0;

int nums[][] = new int[3][5];

// give nums some values

for (int i = 0; i < 3; i++)

for (int j = 0; j < 5; j++)nums[i][j] = (i + 1) * (j + 1);

// use for-each for to display and sum the valuesfor (int x[] : nums) {

for (int y : x) {

System.out.println("Value is: " + y);sum += y;

}

}System.out.println("Summation: " + sum);

}

}

4. 7. 8. Using break with a for-each-style for


public static void main(String args[]) {int sum = 0;

int nums[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

// Use for to display and sum the values.


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for (int x : nums) {

System.out.println("Value is: " + x);sum += x;

if (x == 5){

break; // stop the loop when 5 is obtained

}

}System.out.println("Summation of first 5 elements: " + sum);

}}

Value is: 1


Value is: 4

Value is: 5Summation of first 5 elements: 15

4. 8. Break Statement

4. 8. 1. The break Statement4. 8. 2. Using the break Statement in a Loop: break out from a loop

4. 8. 3. Breaking Indefinite Loops

4. 8. 4. Labelled breaks breaks out of several levels of nested loops inside a pair of curly braces.

4. 8. 5. The Labeled break Statemen

4. 8. 1. The break Statement

The break statement is used to break from an enclosing do, while, for, or switch statement.

It is a compile error to use break anywhere else.

'break' breaks the loop without executing the rest of the statements in the block.For example, consider the following code



int i = 0;while (true) {

System.out.println(i);

i++;if (i > 3) {

break;

}

}}

}The result is

01


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2

3

4. 8. 2. Using the break Statement in a Loop: break out from a loop



int count = 50;

for (int j = 1; j < count; j++) {if (count % j == 0) {

System.out.println("Breaking!!");

break;}

}

}}

Breaking!!

4. 8. 3. Breaking Indefinite Loopspublic class MainClass {


OuterLoop: for (int i = 2;; i++) {

for (int j = 2; j < i; j++) {

if (i % j == 0) {continue OuterLoop;

}

}


if (i == 107) {

break;}

}

}}

2

35

7

11

1317

19

2329

31

3741


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}

System.out.println(i);if (i == 37) {

break OuterLoop;

}

}

}}

23

5

711

13

1719

23

29

3137

4. 9. Continue Statement4. 9. 1. The continue Statement

4. 9. 2. The continue statement: skips all or part of a loop iteration

4. 9. 3. The Labeled continue statement4. 9. 4. Calculating Primes: using continue statement and label

4. 9. 1. The continue Statement

The continue statement stops the execution of the current iteration and causes control to begin with thenext iteration.

For example, the following code prints the number 0 to 9, except 5.



for (int i = 0; i < 10; i++) {

if (i == 5) {continue;

}


}}

}

4. 9. 2. The continue statement: skips all or part of a loop iteration



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for (int i = 1; i


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4. 9. 4. Calculating Primes: using continue statement and label

continue may be followed by a label to identify which enclosing loop to continue to.



int nValues = 50;

OuterLoop: for (int i = 2; i


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System.out.println("This will not be printed.");

} catch (ArithmeticException e) { //System.out.println("Division by zero.");

}

System.out.println("After catch statement.");

}

}

4. 10. 2. Handle an exception and move on.

import java.util.Random;



int a = 0, b = 0, c = 0;Random r = new Random();

for (int i = 0; i < 32000; i++) {

try {b = r.nextInt();

c = r.nextInt();

a = 12345 / (b / c);} catch (ArithmeticException e) {

System.out.println("Division by zero.");

a = 0; // set a to zero and continue}

System.out.println("a: " + a);

}

}}

4. 10. 3. Demonstrate multiple catch statements.class MultiCatch {


try {int a = args.length;

System.out.println("a = " + a);

int b = 42 / a;int c[] = { 1 };

c[42] = 99;

} catch (ArithmeticException e) {

System.out.println("Divide by 0: " + e);} catch (ArrayIndexOutOfBoundsException e) {

System.out.println("Array index oob: " + e);

}System.out.println("After try/catch blocks.");

}

}


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4. 10. 4. Catch different Exception types

class MyException extends Exception {MyException() {

super("My Exception");

}

}

class YourException extends Exception {

YourException() {super("Your Exception");

}

}

class LostException {

public static void main(String[] args) {try {

someMethod1();

} catch (MyException e) {

System.out.println(e.getMessage());} catch (YourException e) {

System.out.println(e.getMessage());

}}

static void someMethod1() throws MyException, YourException {try {

someMethod2();

} finally {

throw new MyException();}

}

static void someMethod2() throws YourException {

throw new YourException();

}}

4. 10. 5. An example of nested try statements.class NestTry {


try {

int a = args.length;

int b = 42 / a;


try {if (a == 1)


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a = a / (a - a); // division by zero

if (a == 2) {

int c[] = { 1 };

c[42] = 99; // generate an out-of-bounds exception

}

} catch (ArrayIndexOutOfBoundsException e) {System.out.println("Array index out-of-bounds: " + e);

}


System.out.println("Divide by 0: " + e);}

}

}

4. 10. 6. Try statements can be implicitly nested via calls to methods

class MethNestTry {

static void nesttry(int a) {try {

if (a == 1)

a = a / (a - a);if (a == 2) {

int c[] = { 1 };

c[42] = 99; // generate an out-of-bounds exception}

} catch (ArrayIndexOutOfBoundsException e) {

System.out.println("Array index out-of-bounds: " + e);

}}

public static void main(String args[]) {try {

int a = args.length;

int b = 42 / a;


nesttry(a);


System.out.println("Divide by 0: " + e);

}}

}

4. 11. throw


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4. 11. 1. Demonstrate throw.

4. 11. 2. Change Exception type and rethrow

4. 11. 1. Demonstrate throw.

class ThrowDemo {

static void demoproc() {

try {throw new NullPointerException("demo");

} catch (NullPointerException e) {System.out.println("Caught inside demoproc.");

throw e; // rethrow the exception

}}

public static void main(String args[]) {try {

demoproc();

} catch (NullPointerException e) {

System.out.println("Recaught: " + e);}

}

}

4. 11. 2. Change Exception type and rethrow

class MyException extends Exception {MyException() {

super("My Exception");

}

}

class YourException extends Exception {

YourException() {super("Your Exception");

}

}

class ChainDemo {

public static void main(String[] args) {try {

someMethod1();

} catch (MyException e) {

e.printStackTrace();}

}

static void someMethod1() throws MyException {

try {

someMethod2();} catch (YourException e) {


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System.out.println(e.getMessage());

MyException e2 = new MyException();e2.initCause(e);

throw e2;

}

}

static void someMethod2() throws YourException {

throw new YourException();}

}

4. 12. finally4. 12. 1. Demonstrate finally.

4. 12. 1. Demonstrate finally.

class FinallyDemo {static void procA() {

try {

System.out.println("inside procA");throw new RuntimeException("demo");

} finally {

System.out.println("procA's finally");}

}

static void procB() {try {

System.out.println("inside procB");

return;} finally {

System.out.println("procB's finally");

}}

static void procC() {try {

System.out.println("inside procC");

} finally {

System.out.println("procC's finally");}

}


try {

procA();} catch (Exception e) {


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System.out.println("Exception caught");

}procB();

procC();

}

}

4. 13. throws signature

4. 13. 1. throws Exception from method

4. 13. 1. throws Exception from method

class ThrowsDemo {static void throwOne() throws IllegalAccessException {

System.out.println("Inside throwOne.");

throw new IllegalAccessException("demo");}


try {throwOne();

} catch (IllegalAccessException e) {

System.out.println("Caught " + e);}

}

}

Date post:	30-May-2018
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