我是Java的新手，因此我仍然掌握了基础知识。我有一个任务，我们需要开发一个程序，计算几代后池塘里的鱼群。虽然代码确实起作用并产生了预期的结果，但我想知道是否有办法不必将系统写入打印两次。那就是我有两个实例，程序将给出答案（如果他们选择'f'则为一个，如果他们选择'v'则为一个）：
// Integer declaration
int istartPop, igrowthRate = 0, igen = 0, igenCount, ifinalPop, ideadFish = 0, MAX_FISH = 5000, imaxFish, MIN_PERCENT = -100, iminPercent, MIN_NO = 0, iminNo;
imaxFish = MAX_FISH;
iminPercent = MIN_PERCENT;
iminNo = MIN_NO;
// Array declaration
int[] iaGrowthRate = new int[20];
// Enabling user to enter data
Scanner inConsole = new Scanner(System.in);
// Welcome Text
System.out.println("Welcome to Population Calculator. \n \nThis program will enable you to calculate the number of fish within a pond. \n \nPlease note: max fish in the pond is " + imaxFish + ".\n");
// Starting population of fish
// Assumption: starting population must be between 0 and 5000
do {
System.out.println("Enter the starting population of fish");
istartPop = inConsole.nextInt();
if (istartPop < iminNo || istartPop > imaxFish)
System.out.println("Please enter a number between 0 and 5000.");
} while(istartPop < iminNo || istartPop > imaxFish);
// Choice of fixed or variable growth rate.
// Ensure only f or v can be entered
System.out.println("Enter F for fixed growth, or V for variable");
String sOption = inConsole.next();
// Calculation and path based on 'f' choice.
// Assumption: growth rate must be greater than or equal to -100% to ensure no negative population.
if (sOption.equals("F") || sOption.equals("f")) {
do {
System.out.println("Enter the growth rate percentage");
igrowthRate = inConsole.nextInt();
if(igrowthRate < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while (igrowthRate < iminPercent);
// Assumption: number of generations must be greater than or equal to 0.
do {
System.out.println("Enter the number of generations");
igen = inConsole.nextInt();
if (igen < iminNo)
System.out.println("Please enter a number greater than or equal to 0.");
} while (igen < iminNo);
// Calculation loop
ifinalPop = istartPop;
for(igenCount = 0; igenCount < igen; igenCount++) {
ifinalPop += ifinalPop * (int)igrowthRate/100;
}
ideadFish = ifinalPop - imaxFish;
if(ifinalPop > imaxFish) {
// Output when population is less than or equal to 5000.
System.out.println ("If you have a starting population of " + istartPop + " and a growth of " + igrowthRate + "%, you will have a final population of " + ifinalPop + " specimens after " + igen + " generations.\nThe habitat capacity of " + imaxFish + " has been reached; " + ideadFish + " fish have died.");
}
// Output when population is greater than 5000.
else {
System.out.println ("If you have a starting population of " + istartPop + " and a growth of " + igrowthRate + "%, you will have a final population of " + ifinalPop + " specimens after " + igen + " generations.");
}
}
// Calculation and path based on 'v' choice
else if (sOption.equals("V") || sOption.equals("v")) {
// Assumption: growth rate must be greater than or equal to -100% to ensure no negative population.
// Enter growth rate for 1st generation.
do {
System.out.println("Enter the growth rate for generation one:");
iaGrowthRate[0] = inConsole.nextInt();
if (iaGrowthRate[0] < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100% \n");
} while(iaGrowthRate[0] < iminPercent);
// Enter growth rate for 2nd generation.
do {
System.out.println("Enter the growth rate for generation two:");
iaGrowthRate[1] = inConsole.nextInt();
if (iaGrowthRate[1] < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while(iaGrowthRate[1] < iminPercent);
// Enter growth rate for 3rd generation.
do {
System.out.println("Enter the growth rate for generation three:");
iaGrowthRate[2] = inConsole.nextInt();
if (iaGrowthRate[2] < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while(iaGrowthRate[2] < iminPercent);
// Enter growth rate for 4th generation.
do {
System.out.println("Enter the growth rate for generation four:");
iaGrowthRate[3] = inConsole.nextInt();
if (iaGrowthRate[3] < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while(iaGrowthRate[3] < iminPercent);
// Enter growth rate for 5th generation.
do {
System.out.println("Enter the growth rate for generation five:");
iaGrowthRate[4] = inConsole.nextInt();
if (iaGrowthRate[4] < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while(iaGrowthRate[4] < iminPercent);
// Enter growth rate for 6th generation.
do {
System.out.println("Enter the growth rate for generation six:");
iaGrowthRate[5] = inConsole.nextInt();
if (iaGrowthRate[5] < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while(iaGrowthRate[5] < iminPercent);
// Enter growth rate for 7th generation.
do {
System.out.println("Enter the growth rate for generation seven:");
iaGrowthRate[6] = inConsole.nextInt();
if (iaGrowthRate[6] < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while(iaGrowthRate[6] < iminPercent);
// Enter growth rate for 8th generation.
do {
System.out.println("Enter the growth rate for generation eight:");
iaGrowthRate[7] = inConsole.nextInt();
if (iaGrowthRate[7] < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while(iaGrowthRate[7] < iminPercent);
// Enter growth rate for 9th generation.
do {
System.out.println("Enter the growth rate for generation nine:");
iaGrowthRate[8] = inConsole.nextInt();
if (iaGrowthRate[8] < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while(iaGrowthRate[8] < iminPercent);
// Enter growth rate for 10th generation.
do {
System.out.println("Enter the growth rate for generation ten:");
iaGrowthRate[9] = inConsole.nextInt();
if (iaGrowthRate[9] < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while(iaGrowthRate[9] < iminPercent);
int iNumElts = 10; // capacity for 20, but only using 10 elements here
ifinalPop = istartPop;
// Body loop
for (int iI = 0; iI < iNumElts; iI++) {
ifinalPop += ifinalPop * (int)iaGrowthRate[iI]/100;
}
ideadFish = ifinalPop - imaxFish;
if(ifinalPop > imaxFish) {
// Output when population is less than or equal to 5000.
System.out.println ("If you have a starting population of " + istartPop + " and a growth of " + igrowthRate + "%, you will have a final population of " + ifinalPop + " specimens after " + igen + " generations.\nThe habitat capacity of " + imaxFish + " has been reached; " + ideadFish + " fish have died.");
}
// Output when population is greater than 5000.
else {
System.out.println ("If you have a starting population of " + istartPop + " and a growth of " + igrowthRate + "%, you will have a final population of " + ifinalPop + " specimens after " + igen + " generations.");
}
}
}
此外，是否可以验证“请输入f或v”以仅允许这些字符。当我尝试像其他人一样做一个while语句时，它会给出一个错误，即字符串'sOption'需要为其所有其他实例重新初始化。任何帮助都会很棒，谢谢
答案 0 :(得分：0)
你可以做的是做一个方法
private void print(String message){
System.out.println(message);
}
并使用您要打印的消息（例如
）调用此方法而不是print语句print("Please enter a number greater than or equal to 0.");
显然，没有办法实际打印它进行打印。
关于验证，您可以像这样使用String类的matches()方法来检查字符串中是否只有f或v
stringToValidate.matches("(f|v)");
答案 1 :(得分：0)
要不要多次写入特定的println()语句，请将其解压缩到方法中并从您需要的位置调用它。
例如：
System.out.println("Enter the growth rate percentage");
可以被提取到
中void printEnterGrowthRate(){
System.out.println("Enter the growth rate percentage");
}
你可以这样调用方法：
printEnterGrowthRate();
这是删除重复的第一步，但您可以更进一步。
查看这些do语句。
这：
do {
System.out.println("Enter the growth rate percentage");
igrowthRate = inConsole.nextInt();
if(igrowthRate < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while (igrowthRate < iminPercent);
和这一个：
do {
System.out.println("Enter the growth rate for generation one:");
iaGrowthRate[0] = inConsole.nextInt();
if (iaGrowthRate[0] < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100% \n");
} while(iaGrowthRate[0] < iminPercent);
和另一个：
do {
System.out.println("Enter the growth rate for generation two:");
iaGrowthRate[1] = inConsole.nextInt();
if (iaGrowthRate[1] < iminPercent)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while(iaGrowthRate[1] < iminPercent);
等......（你有11个喜欢！）
几乎所有东西都是重复的。
您应该引入一个返回int的方法，并在每次需要获取增长率的输入时调用它。然后根据具体情况将int分配给igrowthRate或iaGrowthRate[]。
public int getInputForGrowthRate(String msg, Scanner inConsole){
do {
System.out.println(msg);
int growthRate = inConsole.nextInt();
if (growthRate < MIN_PERCENT)
System.out.println("Please enter a growth rate larger than or equal to -100%");
} while(growthRate < MIN_PERCENT);
return growthRate;
}
您可以替换11组重复的语句来获取输入：
if (sOption.equalsIgnoreCase("f")) {
int igrowthRate = getInputForGrowthRate("Enter the growth rate percentage", inConsole);
...
}
else if (sOption.equalsIgnoreCase("v")) {
String commonMsgPartForMultipleInput = "Enter the growth rate for generation : ";
for (int i=0; i<10; i++){
iaGrowthRate[i] = getInputForGrowthRate(commonMsgPartForMultipleInput + i, inConsole);
}
...
}