createNewFile()和createTempFile()区别 createnewfile失败

createNewFile()和createTempFile()区别：

为了更好地测试，我建了两个类：

1、使用createNewFile()创建一个abc.txt的文件：

1. public class TestFile1 {
2. public static voidmain(String[] args) {
3. File f1 = newFile("C:\abc.txt");
4. try{
5. f1.createNewFile();
6. System.out.println(f1.getName());
7. } catch (IOExceptione) {
8. e.printStackTrace();
9. }
10. }
11. }

public class TestFile1 {                public static void main(String[] args) {                File f1 = new File("C:\abc.txt");                try {                        f1.createNewFile();                        System.out.println(f1.getName());                } catch (IOException e) {                        e.printStackTrace();                }        }}

控制台输出：
abc.txt

2、使用createTempFile()创建一个abc.txt的文件：

1. public class TestFile2 {
2. public static voidmain(String[] args) {
3. File f1 = newFile("C:");
4. File f2 = null;
5. try{
6. f2 = File.createTempFile("abc", ".txt", f1);
7. System.out.println(f2.getName());
8. } catch (IOExceptione) {
9. e.printStackTrace();
10. }
11. }
12. }

public class TestFile2 {                public static void main(String[] args) {                File f1 = new File("C:");                File f2 = null;                try {                        f2 = File.createTempFile("abc", ".txt", f1);                        System.out.println(f2.getName());                } catch (IOException e) {                        e.printStackTrace();                }        }}

控制台输出：
空

但是我查看了指定路径，生成了

abc482578709 1196303263.txt文件，每一次执行，都能生成不同的文件，但中间的数字都是19位，我查看了Java的File源代码，按住Ctrl+鼠标左击，进入File.class，看到有

1. private static File generateFile(String prefix,String suffix, File dir)
2. throwsIOException
3. {
4. long n =LazyInitialization.random.nextLong();
5. if (n ==Long.MIN_VALUE) {
6. n = 0;// corner case
7. } else{
8. n = Math.abs(n);
9. }
10. return new File(dir, prefix + Long.toString(n) +suffix);
11. }

private static File generateFile(String prefix, String suffix, File dir)        throws IOException    {        long n = LazyInitialization.random.nextLong();        if (n == Long.MIN_VALUE) {            n = 0;      // corner case        } else {            n = Math.abs(n);        }        return new File(dir, prefix + Long.toString(n) + suffix);    }

1. public static File createTempFile(String prefix,String suffix,
2. File directory)
3. throwsIOException
4. {
5. if (prefix ==null) throw newNullPointerException();
6. if (prefix.length()< 3)
7. throw newIllegalArgumentException("Prefixstring too short");
8. String s = (suffix == null) ? ".tmp" : suffix;
9. if (directory== null){
10. String tmpDir =LazyInitialization.temporaryDirectory();
11. directory = newFile(tmpDir, fs.prefixLength(tmpDir));
12. }
13. SecurityManager sm =System.getSecurityManager();
14. File f;
15. do{
16. f = generateFile(prefix, s, directory);
17. } while(!checkAndCreate(f.getPath(), sm));
18. returnf;
19. }

    public static File createTempFile(String prefix, String suffix,                                      File directory)        throws IOException    {        if (prefix == null) throw new NullPointerException();        if (prefix.length() < 3)            throw new IllegalArgumentException("Prefix string too short");        String s = (suffix == null) ? ".tmp" : suffix;        if (directory == null) {            String tmpDir = LazyInitialization.temporaryDirectory();            directory = new File(tmpDir, fs.prefixLength(tmpDir));        }        SecurityManager sm = System.getSecurityManager();        File f;        do {            f = generateFile(prefix, s, directory);        } while (!checkAndCreate(f.getPath(), sm));        return f;    }

注意函数generateFile()的返回值是new File(dir, prefix + Long.toString(n) +suffix);

由此可明白为什么会生成abc4825787091196303263.txt文件了。

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