Printstream上的错误.只有最后一句话是书面的

Question

我遇到以下问题。字符串变量打印在txt文件上

```
 1 3 1.
```

实际上，它必须输出

```
1 1 1 
1 2 1
1 3 1
```

我不知道，代码中的错误在哪里。似乎每次代码都在重写，最后一条语句也被重写了。有人能帮我吗

public class RankingExportTest {
private static final String LINE_SEPARATOR = "rn";
Set<String> exportGraph(DirectedUnweightedGraph<CommonNode, CommonEdge<CommonNode>> graph) throws IOException {
Set<String> rows = new LinkedHashSet<>((int)graph.getEdgeCount());
for(CommonNode fromNode: graph.getNodes()) {
 for(CommonNode toNode: graph.adjacentTo(fromNode)) {
            String row = String.format(
                "%d %d 1",
                fromNode.getIdentity().intValue(),
                toNode.getIdentity().intValue()
            );
            rows.add(row);
           System.out.println(row);
            try {
                PrintWriter out;
                out = new PrintWriter( "/Users/......" );
                out.print(rows);
                out.close();
                //System.out.println(row);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }
    }
    return rows;
}

Answer 1

在循环的每次迭代中打开和关闭PrintWriter，每次都覆盖文件。在循环之前打开它，然后关闭它。

Answer 2

您正在用每一行覆盖一个文件。创建PrintWriter一次，写入所有输出，然后关闭它：

PrintWriter out = null;
try {
    out = new PrintWriter("path");
    for (CommonNode fromNode : graph.getNodes()) {
        for (CommonNode toNode : graph.adjacentTo(fromNode)) {
            String row = String.format("%d %d 1", fromNode.getIdentity().intValue(), toNode.getIdentity().intValue());
            rows.add(row);
            System.out.println(row);
            out.print(row);
        }
    }
} catch (FileNotFoundException e) {
    e.printStackTrace();
} finally {
    if (out != null) {
        out.close();
    }
}