java - 如何在不添加尾随逗号的情况下用逗号连接一堆数字？

Question

PrintWriter fout = new PrintWriter(new BufferedWriter(
    new FileWriter("numbers.dat")
)); 
for(int i = start; i <= 100; i = i + 2) { 
    fout.print(i + ", "); 
}

现在我的输出是这样的:

2, 4, 6, 8, 10,

我想要的:

2, 4, 6, 8, 10

Answer 1

这里有一个简洁的方法:

PrintWriter fout = new PrintWriter(new BufferedWriter(
    new FileWriter("numbers.dat")
)); 

String sep = "";
for(int i = start; i <= 100; i += 2) { 
    fout.print(sep + i);
    sep = ", ";
}

另一种方式:

PrintWriter fout = new PrintWriter(new BufferedWriter(
    new FileWriter("numbers.dat")
)); 

for(int i = start; i <= 100; i += 2) { 
    fout.print((i == start ? "" : ", ") + i);
}

---

在不太确定PrintWriter 的功能的情况下，生成带有StringBuffer 的字符串可能更有效。第一:

PrintWriter fout = new PrintWriter(new BufferedWriter(
    new FileWriter("numbers.dat")
));

StringBuffer buffer;

for(int i = start; i <= 100; i += 2) { 
    buffer.append(i == start ? "" : ", ").append(i);
}

fout.print(buffer);

或者更有效:

PrintWriter fout = new PrintWriter(new BufferedWriter(
    new FileWriter("numbers.dat")
));

StringBuffer buffer;

for(int i = start; i <= 100; i += 2) { 
    buffer.append(i).append(", ");
}

buffer.setLength(buffer.length()-1);

fout.print(buffer);