Monthly Archives: October 2013

ArrayList 1 Excercises

BlueJ users. Read this about how to use ArrayLists as parameters. Or consider using Eclipse if this is too much of a hassle.

ArrayList<Integer> factors(int num)

Description: This method returns an ArrayList populated with the factors of num

Method Call	return value/output
factors(5)	{1,5}
factors(10)	{1,2,5,10}

int sum(ArrayList<Integer> nums)

Description: This method returns the sum of all elements in the list

Method Call	return value/output
sum({1,5})	6
sum( { 3,4, 2 } )	9

void printReverse(ArrayList<String> strs)

Description: This method prints all elements in reverse order

Method Call	return value/output
printReverse({“a”,”b”})	“b” “a”
printReverse( “xu”, “t”)	“t” “xu”

double mean(ArrayList<Integer> nums)

Description: This method returns the arithmetic mean of all elements in the list

Method Call	return value/output
mean({1,5})	3
mean( {3,4, 2 } )	4.5

void printEvens(ArrayList<Integer> nums)

Description: This method prints out all even numbers

Method Call	return value/output
printEvens({1,5 , 6})	6
printEvens( {3,4, 2 } )	4 , 2

ArrayList<Double> everyOtherPi(ArrayList<Double> nums )

Description: This method returns a version of the input ArrayList with every other value changed to Math.PI

Do NOT make a new ArrayList in this method

Method Call	return value/output
everyOtherPi ( {1,8,5,0, 7} )	{1, 3.1415 , 5 , 3.1415 , 7 , 3.1415 }
everyOtherPi({0,4,3,5} )	{0, 3.1415 , 3 , 3.1415 }

boolean isIdentical(ArrayList<String> strs1 , ArrayList<String> strs2)

Description: This method returns true if each element in the two ArrayLists is the same

Method Call	return value/output
isIdentical({“ab”, “a”} , { “x”, “a”} )	false
isIdentical({“ab”, “a”} , { “ab”, “a”} )	true
isIdentical({ “xy”} , { “XY”} )	false

int largest(ArrayList<Integer> nums)

Description: This method returns the largest element in nums

Method Call	return value/output
largest({1,5 , 6})	6
largest ({3,4, 2 } )	4

ArrayList<Integer>removeVal(ArrayList<Integer> nums, int val)

Description:This method returns an ArrayList with all instances of val removed

Do NOT make a new ArrayList in this method

Method Call	return value/output
removeVal({1,5 , 6}, 5 )	{1, 6 }
removeVal ( {3,3,3,4, 2} , 3 )	{4,2}

TO do :

PrimesFactory

Matrix Class

Create a class Matrix

int[][] add (int[][] matr1, int[][] matr2)

Description: This method returns the sum of matr1 and matr2

int[][] multiply(int[][] matr1, int[][] matr2)

Description: This method returns the product of matr1 and matr2

2 D Arrays in Java Assignments

Add the following Methods to a class called ArrayFun2D

public void print(int[][] arr)

Description: This method prints each element in the array. This will be a useful method when you are debugging your code and want to test it out to see if it works.

Method Call	return value
print({{1,2} , {3,4}, { 5, 6 } } )	1 2 3 4 5 6

public int sum(int[][] arr)

Description: This method returns the sum of all elements in the array

Method Call	return value
sum({{1,2} , {3,4}, { 5, 6 } } )	21 ( ie 1+2+3+4+5+6)

public String concat(String[][] strs)

Description: This method returns the concatenation of all the elements in the Array

Method Call	return value
concat({{“a”,”xc” }, {“t”, “zoo”}, { “jjkj” } } )	“axctzzoojjkj”

public double mean( int[][] arr)

Description: This method returns the arithmetic mean of the array. Make sure you double check that you are correctly returning results that include decimal values .

Method Call	return value
mean({{2,8} , {4 , 7} } )	5.25 ie (2+8+4+7)/4

public void printRow(int[][] arr, int row)

Description: This method prints all elements in row. This can be (and should be) done with a single loop.

Method Call	return value
printRow({{1,2} , {3,4}, { 5, 6 } } , 1 )	3, 4
printRow( { 5 , 6} , {7, 12, 13 , 5 }, { 5, 6 ,0} } , 2 )	5 , 6, 0

public void printCol(int[][] arr, int col)

Description: This method prints all elements in col.

Method Call	return value
printCol({{1,2} , {3, 4}, { 5, 6 } } , 1 )	2 4 6
printCol( { 5 , 6} , {7, 12, 13 , 5 }, { 12, 6 ,0} } , 0 )	5 7 12
printCol( {12, 13 , 5 }, { 6, 2, 13 ,11} , {1,2 } } , 2 )	5 13

public int maxVal_inRow(int[][] arr, int row)

Description: This method returns the value of the largest number in the given row

Method Call	return value
maxVal_inRow({{1,2} , {3,4}, { 5, 6 } } , 1 )	4
maxVal_inRow ({ { 5 , 6} , {7, 12, 13 , 5 }, { 5, 6 ,0} } , 2 )	6

public int maxVal_inCol(int[][] arr, int col)

Description: This method returns the value of the largest number in the given col

Method Call	return value
maxVal_inCol({{1,2} , {3,4}, { 5, 6 } } , 0 )	5
maxVal_inCol({{1,-2} , {3,-4}, { 5, -5 } } , 1 )	-2

public int[][] changeValues(int[][] table, int val)

Description:This method returns the array with all elements set toval

changeValues(table, 5)

Original Array

1 2

3 4

5 6

Returned Array

5 5

5 5

5 5

public void print_colMajor(int[][] arr)

Description: This method prints each element in the array – using column major order

Method Call	return value
print({{1,2} , {3,4}, { 5, 6 } } )	1 3 5 2 4 6

public int[][] removeVals(int[][] table, int val)

Description: This method returns a version of the 2-d array where val has been removed from all elements

removeValues(table, 5)

Original Array

{1 , 5}

{3, 4}

{5, 6}

Returned Array

{1}

{3, 4}

{6}

int[] twoD_to1D(int[][] arr)

Description: This method takes an input array that is in 2 dimensions and creates a 1 d array . Assume that the array is rectangular (not jagged).

Method Call	return value
twoD_to1D ( {{1,2} , {3,4}, { 5, 6 } } )	{ 1 , 2 , 3 , 4 , 5 , 6 }

Matrices

int[][] add (int[][] matr1, int[][] matr2)

Description: This method returns the sum of matr1 and matr2

how to add matrices

** int[][] multiply(int[][] matr1, int[][] matr2)

Description: This method returns the product of matr1 and matr2

how to multiply matrices

**public int[][] invertValues(int[][] matr)

Description: This method returns the paramater with its values ‘inverted’

Original Array

1 2

3 4

5 6

Returned Array

6 5

4 3

2 1

Two Dimensinal Arrays in Java

Two Dimensional Arrays in Java

  String[][] table =  {
                        {"a","b","c"},
                        {"d","e","f","g"},                        
                        {"g","h"},
                            };

    int table2[][] = {
                        { 1, 4, 5},
                        {5,11,12},                        
                        {22, 45},
                            };

String[][] table = {

{"a","b","c"},

{"d","e","f","g"},

{"g","h"},

};

int table2[][] = {

{ 1, 4, 5},

{5,11,12},

{22, 45},

};

2-D array Demo Code

2 D Array Assignments

Array 3 [ v1]

Warming up

public void printFactors( int n )

Description: This method prints all factors of n

Method Call	return value/output
printFactors( 5)	1 5
printFactors( 6)	1 2 3 6
printFactors( 9 )	1 3 9
printFactors( 15)	1 3 5 15

public int[] getFactors( int n )

Description: This method returns an array populated with the factors on n

Method Call	return value/output
getFactors( 5)	{1,5}
getFactors( 6)	{1,2,3,6}
getFactors( 9 )	{1,3, 9}
getFactors( 15)	{1,3,5}

public int[] removeZeros(int [] nums)

Description: This method returns a version of the input –with all occurrences of 0 , zero, removed

Method Call	return value/output
noZeros( { 3 , 4, 0, 1} )	{ 3, 4, 1}
noZeros( { 0, 5 , 0, 0, 9, 0, 1 , 11} )	{ 5,9,1,11}

** public int[] doubleUp( int [] nums, int val)

Description: This method retuns a version of the input –with all occurances of val duplicated.

Method Call	return value/output
doubleUp( { 3 , 4, 0, 1} , 4 )	{ 3, 4 , 4, 0, 1}
doubleUp( { 1, 3 , 1, 5 , 3, 3} , 3 )	{1 , 3, 3 , 1, 5 , 3, 3, 3, 3 }

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