zoukankan html css js c++ java

java13

TreeSet迭代

 1 import java.util.Iterator;
 2 import java.util.TreeSet;
 3 
 4 public class TreeSetDemo2 {
 5 
 6     public static void main(String[] args) {
 7         TreeSet<String> ts = new TreeSet<String>();
 8         ts.add("tom1");
 9         ts.add("tom3");
10         ts.add("tom2");
11         ts.add("tom5");
12         
13         //得到迭代器
14         Iterator<String> it = ts.iterator();
15         while (it.hasNext()) {
16             String tmp = it.next();
17             System.out.println(tmp);
18         }
19     }
20 
21 }

Map迭代

entry
keySet

valu

 1 import java.util.Collection;
 2 import java.util.HashMap;
 3 import java.util.Iterator;
 4 import java.util.Map;
 5 import java.util.Map.Entry;
 6 import java.util.Set;
 7 
 8 public class HashMapDemo {
 9 
10     public static void main(String[] args) {
11         Map<String, String> map = new HashMap<String, String>();
12         map.put("key001", "tom");
13         map.put("key002", "tom2");
14         map.put("key003", "tom3");
15         map.put("key004", "tom4");
16         map.put("key005", "tom5");
17         map.put("key005", "tom6");
18         
19         //通过Entry迭代
20         Set<Entry<String, String>> set = map.entrySet();
21         Iterator<Entry<String, String>> it = set.iterator();
22         while (it.hasNext()) {
23             Entry <String, String> entry = it.next();
24             String key = entry.getKey();
25             String value = entry.getValue();
26             System.out.println(key + "===" + value);
27         }
28         
29         //通过key迭代
30         Set<String> keySet = map.keySet();
31         Iterator<String> keyIt = keySet.iterator();
32         while (keyIt.hasNext()) {
33             String key = keyIt.next();
34             String value = map.get(key);
35             System.out.println(key + "===" + value);
36         }
37         
38         //通过value迭代
39         Collection<String> valueSet = map.values();
40         Iterator<String> valueIt = valueSet.iterator();
41         while (valueIt.hasNext()) {
42             String value = valueIt.next();
43             System.out.println(value);
44         }
45         
46     }
47 
48 }

装饰模式

实现方式： Buffered类继承Writer类，在类中添加Writer类型的成员变量，对相应方法进行重写时，调用成员变量的方法进行完成。示例如下：

 1 class BufferedWriter extends Writer{
 2     Writer out;
 3     char[] cb = new char[8192];
 4     
 5     public void writer(String str){
 6         // 1.将数据写入缓冲区
 7         cb.xxx
 8         // 2.如果cb已满写入out
 9     }
10     
11     public void close() {
12         // 1.清理cb
13         // 2.关闭out
14     }
15 }

比较FileWriter和BufferedWriter写入效率

 1 import java.io.BufferedWriter;
 2 import java.io.FileWriter;
 3 import java.io.IOException;
 4 
 5 public class CompareBufferedWriter {
 6 
 7     public static void main(String[] args) {
 8         fileWriter();
 9         bufferedWriter();
10     
11 
12     }
13 
14     private static void bufferedWriter() {
15         // BufferedWriter
16         long l = System.currentTimeMillis();
17         String line = System.getProperty("lline.separator");
18         BufferedWriter writer = null;
19         try {
20             writer = new BufferedWriter(new FileWriter("h:\hello2.txt", false));
21             for (int i = 0; i < 10000000; i++) {
22                 writer.write(i + line);
23             }
24         } catch (IOException e) {
25             e.printStackTrace();
26         } finally {
27             if (writer != null) {
28                 try {
29                     writer.close();
30                     System.out.println("BufferedWriter: " + (System.currentTimeMillis() - l));
31                 } catch (IOException e) {
32                     e.printStackTrace();
33                 }
34             }
35         }
36     }
37 
38     private static void fileWriter() {
39         // FileWriter
40         long l = System.currentTimeMillis();
41         String line = System.getProperty("lline.separator");
42         FileWriter writer = null;
43         try {
44             writer = new FileWriter("h:\hello1.txt", false);
45             for (int i = 0; i < 10000000; i++) {
46                 writer.write(i + line);
47             }
48         } catch (IOException e) {
49             e.printStackTrace();
50         } finally {
51             if (writer != null) {
52                 try {
53                     writer.close();
54                     System.out.println("FileWriter: " + (System.currentTimeMillis() - l) );
55                 } catch (IOException e) {
56                     e.printStackTrace();
57                 }
58             }
59         }
60     }
61 
62 }

控制台输出的结果(ms)：

FileWriter: 7925
BufferedWriter: 3902

比较FileReader和BufferedReader的效率

 1 import java.io.BufferedReader;
 2 import java.io.FileNotFoundException;
 3 import java.io.FileReader;
 4 import java.io.IOException;
 5 import java.io.LineNumberReader;
 6 
 7 import org.junit.Test;
 8 
 9 public class BufferedReadTest {
10 
11     public static void main(String[] args) throws Exception {
12         ReadFileNoBuffered();
13         
14         ReadFileWithBuffered();
15         ReadFileWithBuffered2();
16 
17     }
18 
19     private static void ReadFileWithBuffered() throws FileNotFoundException, IOException {
20         BufferedReader br = new BufferedReader (new FileReader("d:\hello.txt"));
21         long start = System.currentTimeMillis();
22         int len = -1;
23         
24         while ((len = br.read()) != -1) {
25             
26         }
27         br.close();
28         System.out.println("ReadFileWithBuffered :" + (System.currentTimeMillis() - start) );
29     }
30 
31     private static void ReadFileNoBuffered() throws FileNotFoundException, IOException {
32         FileReader reader = new FileReader("d:\hello.txt");
33         long start = System.currentTimeMillis();
34         int len = -1;
35         while ((len = reader.read()) != -1) {
36             
37         }
38         reader.close();
39         System.out.println("ReadFileNoBuffered :" + (System.currentTimeMillis() - start) );
40     }
41     /**
42      * 考察磁盘的read性能
43      * @throws FileNotFoundException
44      * @throws IOException
45      */
46     private static void ReadFileWithBuffered2() throws FileNotFoundException, IOException {
47         BufferedReader br = new BufferedReader (new FileReader("d:\hello.txt"));
48         long start = System.currentTimeMillis();
49         int len = -1;
50         char[] cbuf= new char[68888898];
51         br.read(cbuf);
52         br.close();
53         System.out.println("ReadFileWithBuffered2 :" + (System.currentTimeMillis() - start) );
54     }
55     public void hexNum() {
56         int i = 5;
57         i = 0x5;
58         i = -0x5;
59         
60         //byte b = 0x80;//error
61         byte b = -0x80;//- 1000 0000  -128 byte(-128~127)
62     }
63     
64     /**
65      * 测试BufferedReader.readLine()
66      * 取一整行文本
67      * @throws Exception
68      */
69     @Test
70     public void readLineWithBuffered3() throws Exception{
71         BufferedReader br = new BufferedReader(new FileReader("d:\hello.txt"));
72         String line = null;
73         
74         while ((line = br.readLine()) != null){
75             System.out.println(line);
76         }
77         br.close();
78     }
79     
80     /**
81      * 测试LineNumberReader.getLineNumber()
82      * @throws Exception
83      */
84     @Test
85     public void lineNumbreReaderTest() throws Exception{
86         LineNumberReader br = new LineNumberReader(new FileReader("d:\hello.txt"));
87         String line = null;
88         System.out.println(br.getLineNumber());
89         while ((line = br.readLine()) != null){
90             //br.setLineNumber(100);
91             System.out.println(br.getLineNumber());
92         }
93         br.close();
94     }
95 
96 }

控制台输出结果：

ReadFileNoBuffered :8417
ReadFileWithBuffered :1713
ReadFileWithBuffered2 :218

字节流的读写

 1 import java.io.FileInputStream;
 2 import java.io.FileOutputStream;
 3 
 4 import org.junit.Test;
 5 
 6 
 7 public class ByteStreamDemo {
 8     /**
 9      * 复制图片
10      * @author zhengguohuang
11      *
12      */
13     @Test
14     public void copyImage() throws Exception{
15         FileInputStream fin = new FileInputStream("h:\testPicture\clipboard.png");
16         FileOutputStream fout = new FileOutputStream("d:\1.png");
17         
18         byte[] buffer = new byte[1024];
19         int len = -1;
20         while ((len = fin.read(buffer)) != -1) {
21             fout.write(buffer, 0, len);
22         }
23         fin.close();
24         fout.close();
25     }
26 }

字节流

FileInputStream
- 支持skip()方法，skip向后跳的时候不能超过文件头地址，可以超过尾地址
FileOutputStream
- 不支持持skip
RandomAccessFile
- 随机访问文件，定位到文件的任意位置

 1 /**
 2      * 使用文件输出流写文本文件
 3      * 
 4      * @throws Exception
 5      */
 6     @Test
 7     public void writeWithFileOutputStream() throws Exception {
 8         System.out.println(Charset.defaultCharset());
 9         FileOutputStream fos = new FileOutputStream("d://hello.txt");
10 
11         String str = "你adaac";
12         // 编码7 bytes
13         // fos.write(str.getBytes("GBK"));
14         // 编码6 bytes
15         // fos.write(str.getBytes("ios8859-1"));
16 
17         // 编码8 bytes
18         fos.write(str.getBytes("utf-8"));
19         fos.close();
20         System.out.println("over");
21     }
22 
23     /**
24      * 使用文件输入流读取文本
25      * @throws Exception
26      */
27     @Test
28     public void readFileWithFileInputStream() throws Exception {
29         FileInputStream fis = new FileInputStream("d://hello.txt");
30         char c = (char)fis.read();//读一个字节
31         fis.skip(3);//跳过三个字节，可前可后
32         c = (char)fis.read();//读一个字节
33         System.out.println(c);
34     }

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原文地址：https://www.cnblogs.com/8386blogs/p/7505701.html