Routines: Void Methods in Java

Routines: Void Methods in Java Methods are the basic Big building blocks of programs. Methods are often called sub-Programs or procedures. There are two very different kinds of methods: functions, also called type methods, and routines, also called void methods. Void methods will be considered here first; type methods come later. Void methods do some action (called a side-effect); they do not return any value; Type methods return some value; they do not do an action. Examples of void methods include output methods such as: outputInt, outputDouble, outputString, outputlnInt, etc. Such void methods stand alone, and end with a semicolon; they are not parts of other expressions. Definition of other void methods will be done here. Many of these methods will also involve outputs, such as: outRow (many, mark), which outputs a row of many marks, spellout (number), which spells out a number in English, formatMoney (amount) which prints an amount in a good form, sidePlot() plots out some arithmetic functions or formulas. 1 OutRow (num, str) is an example of a void method that involves two slots num and str (often called parameters or arguments). When this method is used or called in a command like: outRow (7, "Ho "); it prints out the string "Ho "for a total of 7 tmes in a row, as: Ho Ho Ho Ho Ho Ho Ho Similarily, the call outRow(30, "-") outputs a row of 30 dashes as follows: ----------------------------Externally, this method can be viewed as a black box, Graphic of a void method which has two input slots (also called parameters): a, is an integer number of repetitions, and Data flow view (external) b, is the string which is being repeated. a 3 n Internally the two slots are labelled n and s, outRow b "*" s Use: outRow (a, b); Data space view (internal) a 15 b “-” s n count 15 local and there is a matching between these two; a is passed to n, and b is passed to s. The order is very important, so that outRow ("Ho ", 30); has no meaning, and is an error; the number is expected first. Local, or temporary boxes include the count, which is hidden from the outside. Another box outside of this method may have this same name, count. 2 Definition of a void method is shown below; it consists of two main parts: Header is the part which gives the name, list of slots, and goal is shared with others; Body is the part with local or temporary boxes and local actions which are hidden from others. Syntax of void method definition void name ( Example: outRow void method header type-name pairs (comma separated) Documentation ) { slots (args) pass in Goal & contract Box declarations local boxes Actions body }//end void method name end void outRow ( int n, String s ) { // Does output n strings s // not followed by a new line // Need integer n, (n >= 0) int count; count = 0 Share WHAT Hide HOW while (count < n) { JJS.outputString (s); count ++; }//end while // can put newline here }//end void method outRow The header provides a contract between the creator and user of a method. Does, is also called a post-condition; it indicates the outcome of the method. Need, is a pre-condition, indicating what the method requires to satisfy the contract. In this case the number of repetitions, n, must be a non-negative integer. If n is provided as a real value, or a string, or boolean or negative the contract is broken. 3 Syntax of a void method is shown below, at the left;Two examples of void methods are at the right. main0 calls outRow(5, “Ho “) to print out a row of 5 Hos, “Ho Ho Ho Ho Ho”. It also underlines them. void name ( slotList ) type nameList { ; void main0() { int count; // Does reuse outRow method JJS.start(); outRow (5,"Ho "); JJS.outputlnString ("");//newline // Does description outRow (14,"-" ); JJS.outputlnString (" "); }//end void method main0 JJS.start(); //one main actions }//end void method name JJS.start() is a command that can appear in at most one void method; It indicates the starting method, and is usually in the main void method. void outRow (int many, String marks) { int count; // Does output a row of many marks // Needs (many >= 0) count = 0; while (count < many) { JJS.outputString (marks); count = count + 1; }//end while }//end void method outRow Ho Ho Ho Ho Ho -------------- 4 Another example of a main program using the outRow method follows. It prompts for string, enters it, and “sandwiches” the whole string. // Name An Onymous void main1() { int len; String str; // Does "box" a string using outRow JJS.start(); JJS.outputlnString ("Enter any string "); str = JJS.inputString(); JJS.outputlnString (str); void outRow (int many, String marks) { int count; // Does output a row of many marks // Needs (many >= 0) count = 0; while (count < many) { JJS.outputString (marks); count = count + 1; }//end while }//end void method outRow len = str.length(); // output a row of dashes (-) outRow (len, "-"); JJS.outputlnString(" "); JJS.outputlnString(str); Enter a string Once upon a time there lived 3 bulls -----------------------------------Once upon a time there lived 3 bulls ==================================== // Output a row of equals (=) outRow (len, "="); JJS.outputlnString(" "); }//End void method main1 5 Spellout(number) is a routine which prints out the passed number in English. // Name An Onymous void main2() { int number; // Does spell out some small numbers JJS.start(); JJS.outputlnString ("Enter an integer "); number = JJS.inputInt (); Enter an integer 2 two spellOut (number); JJS.outputln(); }//end void method main2 Enter an integer -2 -2 Enter an integer 4 4 void spellOut (int num) { //no local, temporary boxes // Needs positive int (0 to 3) // Does write out the int number if (num == 0) { JJS.outputString ("zero " ); }else if (num == 1) { JJS.outputString ("one " ); }else if (num == 2) { JJS.outputString ("two " ); }else if (num == 3) { JJS.outputString ("three "); //grow more here }else{ JJS.outputInt (num); }//end if }//end void method spellOut 6 // Name An Onymous void main3() { int num, tens, units; // Does write ints 0 to 100 in English JJS.start(); JJS.outputlnString ("Enter an int: "); num = JJS.inputInt (); if (num < 10) { spellDigit (num); }else if (num < 20) { spellTeen (num); }else{ tens = num / 10; spellTens (10 * tens); units = (num % 10); if ( (units) != 0) { spellDigit (units); }//end if }//end if }//end void method main3 void spellDigit (int num) { // Need (0 <= num) && (num < 10) // Does write digits 0 to 9 in English void spellTeen (int num) { // Need (11 <= num) && (num < 20) // Does write numbers 11 to 19 in English void spellTens (int num) { // Need (10 <= num) && (num < 100) && // Does write out int numbers 10 to 99 Enter an int: 0 zero Enter an int: 13 thirteen Enter an int: 30 thirty Enter an int: 53 fifty three Enter an int: 123 ???? three Does show the use of three methods (given as stubs , not in detail) defined by assertions: Does: is a post-condition Need: is a pre-condition SpellDigit has details which are very similar to spellOut; you do the others. 7 // Name An Onymous void main4() { double amt; // Does show use of formatMoney method JJS.start() { FormatMoney prints out money amounts in a proper way. JJS.outputlnString ("Enter dollars "); amt = JJS.inputDouble (); formatMoney (amt); JJS.outputString ("\n"); }//end void method main4 void formatMoney (double amt) { int iAmt, dollars, cents; // Does write money in form $ddd.cc // Need real input (amt >= 0.0) amt = 100.0 * amt; // in cents iAmt = JJS.doubleToInt (amt + 0.5); cents = iAmount % 100; JJS.outputString ("$"); //Optional JJS.outputDouble (dollars); JJS.outputString ("."); if (cents <= 9) { JJS.outputString ("0"); }//end if cents is small JJS.outputInt (cents); }//end void method formatMoney Enter dollars 1234.567 $1234.57 Enter dollars 1.2 $1.20 Enter dollars 0.1 $0.10 Enter dollars 0.995 $1.00 8 SidePlot, another way to use outRow // Name An Onymous void main5() { double x,y; //real values int iY; //rounded y // Does a side plot of y = f(x) using JJS.start() { x = 0.0; while (x <= 6.0) { // Compute y and digitize it to iY y = 2*x*x; //f(x) is quadratic iY = JJS.doubleToInt (y + 0.5); outRow (iY, " "); JJS.outputString ("o"); JJS.outputString ("\n"); x = x + 0.5; }//end while }//end void method main5 o o o outRow o o o o // // // // round blanks do mark newline void outRow (int many, String marks) { // Does output a row of many marks // without using any local boxes // Not in APJS,as slots are changed! while (many != 0) { JJS.outputString (marks); many = many - 1; }//end while }//end void method outRow (ultimate output; you enhance it so) +--------------------------------------------------+ |0 | |0 | | 0 | | 0 | | 0 | | 0 | | 0 | | 0 | | 0 | | 0 | | 0 | | 0 | | 0 | | 0 | | 0| +- - - - - + - - - - + - - - - + - - - - + - - - - + 012345678901234567890123456789012345678901234567890 9 Many ways to do outRow (including the For and recursion). // Name An Onymous void main6() { int num; //number of repetitions String str; //string to be repeated // Does show many ways to do outRow method JJS.start() { JJS.outputlnString ("Enter an integer "); num = JJS.inputInt (); JJS.outputlnInt (num); JJS.outputlnString ("Enter any string "); str = JJS.inputString (); JJS.outputlnString (str); outRow (num, st); JJS.outputString("\n"); }//end void method main6 Enter an integer 7 Enter a string ----+ ----+----+----+----+----+----+----+ void outRow (int many, String marks) { // Does output a row of many marks // Uses the For loop for (int i = 0; i < many; i++) { JJS.outputString (marks); }//end for }//end void method outRow In the following version, note that outRow calls itself (called recursion) but with different slots each time. Try to trace it. void outRow (int many, String marks) { // Does output a row of many marks // using recursion, calling itself! // Need (many >= 0) if (many != 0) { JJS.outputString (marks); outRow (many - 1, marks); }//end while }//end recursive method outRow 10 Problems on Routines 1.More SpellOut Enhance the SpellOut routine to spell more values , up to 10. 2. SpellTeen Stubs Complete the stubs to spell out the teens (11 to 19). 3. SpellTens ReUse spellDigit and spellTeen to spell out ints from 0 to 99. 4. Format Gas Change FormatMoney to format any reals to three decimal points. 5. Break Greetings Use outRow to display a greeting (say “Happy Anniversary”) by writing many lines, but putting a gap after every fifth one. 6. OutGreetPair ReUse outRow to output a string greeting, two to a line. For example “Happy Birthday” can be written 21 as 10 full lines with one half line. 11 Short Routines It may be convenient to write various common commands in a short way. For example, rather than writing JJS.outputString(s) or System.out.print(s) a shorter way would be to create a void method outStr and Re-call it often: outStr(s); Write void methods for the following outStr(s) which is a simple way to call to output a specified string. outLnStr(s) which outputs a string followed by a new line outLine() which is a short way to output a new line, outLnInt(I) which outputs an int followed by a new line outIntSpace(i) which prints an int i followed by a space (not a new line) outPrompt(s) which prints out the specified prompt (followed by new line) outReal(r) which prints out a real value r followed by a space Do also some of your own. 12 HelplFul Routines Write routines to display the following; You need not include all the details (exclude the repeated parts) 1. outWeek(day) which prints out “Sunday” for day 0, etc.. 2. outWeek1(day) which outputs “Sunday” for day 1, etc… Hint: ReUse! 3. outMonth(num) which prints out “January” for day 1, etc.. 4. outMorse(digit) which prints out a given digit in Morse code. 13 BIG-DIGITS 1. DrawADigit Write a method drawDigit(d) which draws the decimal digit specified but on it’s side consisting of “Bixels” 8 high. For example drawDigit(4) draws the following: 0000 0 00000000 2. drawPercent Write another method drawPercent(p) which draws any percentage p (from 0 to 100) as a series of 1, 2, or 3 such bigDigits on their side. 3. drawInt Write another method drawInt(i) which draws any given integer i as a bigInt. 4. drawChr(c) Write many method to draw a given capitalized character from “A” to “Z”; This may be best done with a team. 5. More For BigDigits; Include the outPeriod(), outDollar(), outSpace, outSpaces(n), etc 14 More draw Routines 1. drawBigTime(mil) for given military time mil. 2. drawBigLowerLetters(low): bigger team for all 16 lower case letters, But done with a total height of 12 bixels. 3. drawBigLetter(x): team project for all 26 capital letters of the alphabet. 4. drawADie(dots), showing any of the 6 faces, such as +-------+ | 0 0 0 | | | | 0 0 0 | +-------+ 5. DrawATotem Pole 15