我怎樣才能在 Java 中使用任何替代“goto”的方法？我嘗試使用中斷標(biāo)簽。但是由于我沒(méi)有跳出任何循環(huán)，所以它給出了未定義的標(biāo)簽錯(cuò)誤。import java.io.*;class $08_02_Total_Avg_Marks{ public static void main(String args[]) throws IOException { //declare and initialize variables int subNo = 0, totalMarks = 0; float avg = 0.0F; BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); label1: System.out.println("Enter no. of subjects"); //check if input is integer try { subNo = Integer.parseInt(br.readLine().trim()); } catch(NumberFormatException e) { System.out.println("Please enter a whole number."); //goto label1 } int[] marksArray = new int[subNo]; for(int i=0; i<marksArray.length; i++) {label2: System.out.println("Enter marks for subject " + (i+1)); try { marksArray[i] = Integer.parseInt(br.readLine().trim()); } catch(NumberFormatException e) { System.out.println("Please enter a whole number."); //goto label2 } }}}我正在終止無(wú)效輸入的程序。但是我需要在無(wú)效輸入上執(zhí)行相同的行。
4 回答
斯蒂芬大帝
TA貢獻(xiàn)1827條經(jīng)驗(yàn) 獲得超8個(gè)贊
與其明確地轉(zhuǎn)到特定點(diǎn)，不如將您可能想要在循環(huán)中重復(fù)的位包裝起來(lái)。如果您不想再次執(zhí)行循環(huán)，break.
對(duì)于第一個(gè)：
while (true) {
System.out.println("Enter no. of subjects");
//check if input is integer
try
{
subNo = Integer.parseInt(br.readLine().trim());
break;
}
catch(NumberFormatException e)
{
System.out.println("Please enter a whole number.");
// Nothing required to continue loop.
}
}
對(duì)于第二個(gè)，將循環(huán)體包裹在循環(huán)中：
for(int i=0; i<marksArray.length; i++)
{
while (true) {
System.out.println("Enter marks for subject " + (i+1));
try
{
marksArray[i] = Integer.parseInt(br.readLine().trim());
break;
}
catch(NumberFormatException e)
{
System.out.println("Please enter a whole number.");
}
}
}
或者，寫(xiě)一個(gè)包裝這個(gè)循環(huán)的方法可能更好：
int getInt(BufferedReader br) throws IOException {
while (true) {
try
{
return Integer.parseInt(br.readLine().trim());
} catch(NumberFormatException e) {
System.out.println("Please enter a whole number.");
}
}
}
然后調(diào)用此方法：
System.out.println("Enter no. of subjects");
int subNo = getInt(br);
for(int i=0; i<marksArray.length; i++) {
System.out.println("Enter marks for subject " + (i+1));
marksArray[i] = getInt(br);
}
慕碼人2483693
TA貢獻(xiàn)1860條經(jīng)驗(yàn) 獲得超9個(gè)贊
我已經(jīng)稍微重新格式化了您的代碼。我的基本想法是：所有的 goto 語(yǔ)句都可以寫(xiě)成等價(jià)的循環(huán)。第一個(gè)現(xiàn)在是用一個(gè) while 循環(huán)制作的，它終止了一個(gè)沒(méi)有例外。至于第二個(gè)標(biāo)簽，它是用相同的機(jī)制完成的（所以是一個(gè) while 循環(huán)），但是，標(biāo)簽可以用“break + nameOfYourLable” - 語(yǔ)句退出/終止。
import java.io.*;
class $08_02_Total_Avg_Marks
{
public static void main(String args[]) throws IOException
{
//declare and initialize variables
int subNo = 0, totalMarks = 0;
float avg = 0.0F;
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
boolean goToLabel1 = true;
while (goToLabel1) {
System.out.println("Enter no. of subjects");
//check if input is integer
try
{
subNo = Integer.parseInt(br.readLine().trim());
goToLabel1 = false; //parsing succeeded, no need to jump to label1
}
catch(NumberFormatException e)
{
System.out.println("Please enter a whole number.");
//goto label1
}
}
int[] marksArray = new int[subNo];
for(int i=0; i<marksArray.length; i++)
{
label2: while (true) {
System.out.println("Enter marks for subject " + (i+1));
try
{
marksArray[i] = Integer.parseInt(br.readLine().trim());
break label2;
}
catch(NumberFormatException e)
{
System.out.println("Please enter a whole number.");
}
}
}
}
}
搖曳的薔薇
TA貢獻(xiàn)1793條經(jīng)驗(yàn) 獲得超6個(gè)贊
此代碼片段將循環(huán)直到插入正確的數(shù)字，在本例中（它解決了您的第一個(gè) goto 問(wèn)題）
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
boolean noNumberEntered; //Default on false
System.out.println("Enter no. of subjects");
//TODO: check if input is integer
while(!noNumberEntered){
try
{
subNo = Integer.parseInt(br.readLine().trim());
noNumberEntered = true;
}
catch(NumberFormatException e)
{
System.out.println("Please enter a whole number.");
}
}
翻閱古今
TA貢獻(xiàn)1780條經(jīng)驗(yàn) 獲得超5個(gè)贊
您可以改用do while循環(huán)和布爾值，如下所示：
class $08_02_Total_Avg_Marks
{
public static void main(String args[]) throws IOException
{
//declare and initialize variables
int subNo = 0, totalMarks = 0;
float avg = 0.0F;
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
boolean goodEntry = true;
do {
goodEntry = true;
System.out.println("Enter no. of subjects");
//check if input is integer
try
{
subNo = Integer.parseInt(br.readLine().trim());
}
catch(NumberFormatException e)
{
System.out.println("Please enter a whole number.");
goodEntry = false;
}
} while(!goodEntry);
}
你可以對(duì)你的第二個(gè)做同樣的事情goto。有很多方法可以做到這一點(diǎn)（使用while循環(huán)和布爾值，使用breaks...），但循環(huán)比goto.
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