字符串(String)

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 /**
 4  * 通过字符串函数 substring() 函数来删除字符串中的一个字符，我们将功能封装在 removeCharAt 函数中
 5  */
 6 public class DeleteStr {
 7     public static void main(String[] args){
 8         test1();
 9         test2();
10     }
11     //方法一
12     private static void test1(){
13         String startStr = "there is java";
14         String endStr = startStr.substring(0, 3) + startStr.substring(4);
15         System.out.println("This is test1 :");
16         System.out.println(endStr);
17     }
18     //方法二
19     private static void test2(){
20         String str = "there is java";
21         System.out.println("This is test2 :");
22         System.out.println(removeStr(str, 3));
23     }
24     public static String removeStr(String str, int pos){
25         return str.substring(0, pos) + str.substring(pos + 1);
26     }
27 }

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 /**
 4  * 通过字符串函数 strOrig.lastIndexOf(StringName) 来查找子字符串 StringName 在 strOrig 出现的位置
 5  */
 6 
 7 public class LastIndexOf {
 8     public static void main(String[] args){
 9         String strOrig = "Hello World, Hello Java";
10         String strIndex = "Hello";
11         int lastIndex = strOrig.lastIndexOf(strIndex);
12         if (lastIndex == -1) System.out.println(strIndex + " Not Found");
13         else System.out.println("Last occurrence of " + strIndex + " is at index "
14                 + lastIndex);
15     }
16 }

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 /**
 4  * 通过 "+" 操作符和StringBuffer.append() 方法来连接字符串，并比较其性能
 5  */
 6 public class StrAdd {
 7     public static void main(String[] args){
 8         long startTime1 = System.currentTimeMillis();
 9         for(int i = 0; i < 5000; i++){
10             String result = "This" + "Is" + "Testing" + "The" +
11                     "Different" + "Between" + "String" + "And" + "StringBuffer";
12         }
13         long endTime1 = System.currentTimeMillis();
14         System.out.println("使用 + 操作符:" + (endTime1 - startTime1) + "ms");
15 
16         long startTime2 = System.currentTimeMillis();
17         for(int i = 0; i < 5000; i++){
18             StringBuffer result = new StringBuffer();
19             result.append("This");
20             result.append("Is");
21             result.append("Testing");
22             result.append("The");
23             result.append("Difference");
24             result.append("Between");
25             result.append("String");
26             result.append("And");
27             result.append("StringBuffer");
28         }
29         long endTime2 = System.currentTimeMillis();
30         System.out.println("使用StringBuffer.append()连接:" + (endTime2 - startTime2) + "ms");
31     }
32 
33 }

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 /**
 4  * 通过 String.intern() 方法来优化字符串
 5  */
 6 public class StrBecomeBest {
 7     public static void main(String[] args){
 8         String[] variables = new String[50000];
 9         long startTime0 = System.currentTimeMillis();
10         for (int i = 0; i < 50000; i++){
11             variables[i] = "s" + i;
12         }
13         long endTime0 = System.currentTimeMillis();
14         System.out.println("Creation time of String literals :" + (endTime0 - startTime0)
15          + "ms");
16 
17         long startTime1 = System.currentTimeMillis();
18         for (int i = 0; i < 50000; i++){
19             variables[i] = new String("hello");
20         }
21         long endTime1 = System.currentTimeMillis();
22         System.out.println("Creation time of String objects with ‘new‘ key word :" +
23                 (endTime1 - startTime1) + "ms");
24 
25         long startTime2 = System.currentTimeMillis();
26         for (int i = 0; i < 50000; i++){
27             variables[i] = new String("hello");
28             variables[i] = variables[i].intern();
29         }
30         long endTime2 = System.currentTimeMillis();
31         System.out.println("Creation time of String objects with intern() :" +
32                 (endTime2 - startTime2) + "ms");
33     }
34 }

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 import java.util.Locale;
 4 
 5 /**
 6  * 通过 format() 方法来格式化字符串，还可以指定地区来格式化
 7  */
 8 public class StrFormat {
 9     public static void main(String[] args){
10         double e = Math.E;  //自然对数e
11         System.out.format("%f%n", e);
12         System.out.format(Locale.GERMANY, "%-10.4f%n%n", e);
13     }
14 }

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 /**
 4  * 通过两种方式创建字符串，并测试其性能
 5  */
 6 public class StrFunctionCompare {
 7     public static void main(String[] args){
 8         long startTime1 = System.currentTimeMillis();
 9         for(int i = 0; i < 50000; i++) {
10             String s1 = "hello world";
11             String s2 = "hello java";
12         }
13             long endTime1 = System.currentTimeMillis();
14             System.out.println("通过String关键字创建字符串耗时 " + (endTime1 - startTime1) + "毫秒");
15 
16             long startTime2 = System.currentTimeMillis();
17             for(int i = 0; i < 50000; i++){
18                 String s3 = new String("hello java");
19                 String s4 = new String("hello world");
20             }
21             long endTime2 = System.currentTimeMillis();
22             System.out.println("通过String对象创建创建字符串耗时  " + (endTime2 - startTime2) + "毫秒");
23     }
24 }

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 /**
 4  * 使用 regionMatches() 方法测试两个字符串区域是否相等
 5  */
 6 public class StrIfSame {
 7     public static void main(String[] args){
 8         String str1 = "Welcome to Microsoft";
 9         String str2 = "I work with microsoft";
10         boolean match1 = str1.regionMatches(true, 11, str2, 12, 9);
11         boolean match2 = str1.regionMatches(false, 11, str2, 12, 9);
12         System.out.println("区分大小写:" + match2);
13         System.out.println("不区分大小写:" + match1);
14     }
15 }
16 
17 
18 /*
19 * str1.regionMatches(11, str2, 12, 9)
20 * 表示将 str1 字符串从第11个字符"M"开始和 str2 字符串的第12个字符"m"开始逐个比较，共比较 9 对字符
21 * 如果设置第一个参数为 true ，则表示忽略大小写区别,反之则区分大小写
22 *
23 * */

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 /**
 4  * 通过字符串函数 compareTo (string) ，compareToIgnoreCase(String) 及 compareTo(object string)
 5  * 来比较两个字符串，并返回字符串中第一个字母ASCII的差值。
 6  */
 7 public class StringCompare {
 8     public static void main(String[] args){
 9         String str = "Hello World";
10         String anotherString = "hello world";
11         Object objStr = str;
12 
13         System.out.println(str.compareTo(anotherString));   // -32
14         System.out.println(str.compareToIgnoreCase(anotherString)); // 0
15         System.out.println(str.compareTo(objStr.toString()));   // 0
16 
17         System.out.println("He".compareToIgnoreCase("hD"));     // 1
18         System.out.println("Hed".compareToIgnoreCase("hEq"));   // -13
19     }
20 }
21 
22 
23 /*
24 * 总结:
25 * A and B both string
26 *
27 * 1 比较两个字符串首字母的ASCII码差值
28 *   A.compareTo(B)
29 * 2 忽略大小写并比较两个字符串首字母的ASCII码差值,若两字母顺位字母相同，则比较下一位，直至相同位置出现不同字母
30 *   A.compareToIgnoreCase(B)
31 *
32 * */

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 /**
 4  * 使用 java String 类的 replace 方法来替换字符串中的字符
 5  */
 6 public class StrReplace {
 7     public static void main(String[] args){
 8         String str = "Hello World, Hello Java, Hello !";
 9         System.out.println(str.replace(‘H‘, ‘W‘));      //替换所有
10         System.out.println(str.replaceFirst("He", "WW"));   //替换首个
11         System.out.println(str.replaceAll("He", "HH"));     //替换所有
12     }
13 }

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 /**
 4  * 使用 Java 的反转函数 reverse() 将字符串反转
 5  */
 6 
 7 public class StrReverse {
 8     public static void main(String[] args){
 9         String startStr = "this is java!";
10         String endStr = new StringBuffer(startStr).reverse().toString();
11         System.out.println("String before reverse :" + startStr);
12         System.out.println("String after reverse :" + endStr);
13     }
14 }

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 /**
 4  * 使用了 String 类的 indexOf() 方法在字符串中查找子字符串出现的位置，
 5  * 如过存在返回字符串出现的位置（第一位为0），如果不存在返回 -1
 6  */
 7 public class StrSearch {
 8     public static void main(String[] args){
 9         String str = "There is no people";
10         String indexStr = "no";
11         int indexNumber = str.indexOf(indexStr);
12         if(indexNumber != -1)
13         System.out.println("Found ‘" + indexStr + "‘ At Index ‘" + indexNumber);
14         else System.out.println( "‘" + indexStr + "‘ Is Not Found In String ‘" + str + "‘");
15     }
16 }

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 /**
 4  * 使用 split(string) 方法通过指定分隔符将字符串分割为数组
 5  */
 6 
 7 public class StrSplit {
 8     public static void main(String[] args){
 9         String str = "www.w3cSchool.com";
10         String[] temp1, temp2;
11         String splitStr = "\\.";    //需要转义字符进行转义
12         temp1 =str.split(splitStr);
13         System.out.println("----- for 方式 -----");
14         for (int i = 0; i < temp1.length; i++){
15             System.out.println(temp1[i]);
16         }
17         System.out.println("----- foreach 方式 -----");
18         temp2 = str.split(splitStr);
19         for (String x:temp2)
20             System.out.println(x);
21 
22 
23 
24 
25     }
26 }

 1 package JavaEE.JavaBaseExampleTest.Str;
 2 
 3 /**
 4  * 使用 String toUpperCase() 方法将字符串从小写转为大写
 5  * 使用 String toLowerCase() 方法将字符串从大写转为小写
 6  */
 7 public class UpToLow {
 8     public static void main(String[] args){
 9         String strSmall = "strIng apPle tO be Upper";
10         String strBig = "THis iS UppER";
11         String upperStr = strSmall.toUpperCase();
12         String lowerStr = strBig.toLowerCase();
13         System.out.println("‘" + strSmall + "‘ Upper Is ‘" + upperStr);
14         System.out.println("‘" + strBig + "‘ Lower Is ‘" + lowerStr);
15 
16     }
17 }