String类
必须会,会到什么程度,会到查看API文档,不用eclipse就可以说出怎么运用String里面的函数,不然你说有开发经验,别人都不会相信
1. String s1 = "abc"; //s1是一个类类型的变量,"abc"是一个对象; 2. //字符创最大的特点:一旦被初始化就不可以改变,因为String类被finally修饰 3. String s2 = new String("abc"); 4. //一个面试题:上面的s1和s2有什么区别 5. //s1在内存中有一个对象; 6. //s2在内存中有两个对象. 7. System.out.println(s1==s2); //结果为false,因为上面的是两个对象,它们的地址值不同,s1和s2为它们的地址值,所以不相等 8. System.out.println(s1.equals(s2));//结果为true,因为在String类中复写了Object类中的equals()方法, 9. //该方法判断字符串里面的内容是否相等,在Object类中的equals()方式是比较对象的地址值 10. String s3 = "abc"; 11. System.out.println(s1==s3);//结果为true,因为在内存中,为了节省空间,它们两个一样,就直接s3指向了s1建立的"abc"对象
一.String类中常见的操作
1.获取
1. 1.1 字符串的长度 2. int length():获取长度 3. 1.2 根据位置获取位置上的某个字符 4. char charAt(int index) 5. 1.3 根据字符串获取该字符在字符串中的位置 6. int indexOf(int ch):返回的是ch在字符串中第一次出现的位置 7. int indexOf(int ch,int fromIndex):从fromIndex指定位置开始,获取ch在字符串中出现的位置 8. 9. int indexOf(String str):返回字符串str在字符串中第一次出现的位置 10. int indexOf(String str,int fromIndex):从fromIndex指定位置开始,获取字符串str在字符串中出现的位置 11. 12. int lastIndexOf(int ch):反向索引,返回ch第一次出现的位置
2.判断
1. 2.1 字符串是否包含某个子串 2. boolean isEmpty() 3. 2.2 字符串中是否有内容 4. boolean contains(String str) 5. int indexOf(String str):索引str第一次出现的位置,如果返回-1,表示str在字符串中不存在,这样也能判断字符串中是否含有该str 6. 2.3 字符串是否是以指定内容开头 7. boolean startsWith(String str) 8. 2.4 字符串是否是以指定内容结尾 9. boolean endsWith(String str) 10. 2.5 判断字符串内容是否相等,复写了Object类中的equals方法 11. boolean equals(String str) 12. 2.6 判断内容是否相同,并忽略大小写 13. boolean equalsIgnoreCase()
3.转换
1. 3.1 将字符数组转成字符串 2. 构造函数:String(char[]) 3. String(char[],offset,count):将字符数组中的一部分转成字符串,offset为起始位置索引,count为个数 4. 静态方法:static String copyValueOf(char[]) 5. static String copyValueOf(char[] data,int offset,int count) 6. static String valueOf(char[]) 7. 3.2 将字符串转成字符数组 8. char[] toCharArray() 9. 3.3 将字节数组转成字符串 10. String(byte[]) 11. String(byte[] data,int offset,int count) 12. 3.4 将字符串转成字节数组 13. byte[] getBytes(),特殊:字符串和字节数组在转换过程中,是可以指定编码表的 14. 3.5 将基本数据类型转成字符串 15. static String valueOf(int) 16. static String valueOf(double)
4.替换
1. String replace(char oldChar,char newChar):也可以替换字符串
5.分割
1. String[] split(regex):将regex作为分隔符来分割字符串,返回字符串数组
6.子串
1. String substring(begin index):获取字符串从指定位置开始到结尾 2. String substring(begin index ,end index):包含头,不包含尾
7.转换,去除空格,比较
1. 7.1 将字符串转成大写或者小写 2. String toUpperCase(); 3. String toLowerCase(); 4. 7.2 将字符串两端的多个空格去除 5. String trim(); 6. 7.3 对两个字符串进行自然顺序的比较 7. int compareTo(String str);
二.程序实例
1.class StringDemo 2.{ 3. public static void main(String[] args) 4. { 5. method_7(); 6. method_sub(); 7. method_split(); 8. method_replace(); 9. method_trans(); 10. method_is(); 11. method_get(); 12. 13. 14. } 15. public static void method_7() 16. { 17. String s = " HolLo JaVa "; 18. String s1 = s.toUpperCase(); 19. String s2 = s.toLowerCase(); 20. String s3 = s.trim(); 21. String s4 = "abc"; 22. String s5 = "aaa"; 23. sop(s1); 24. sop(s2); 25. sop(s3); 26. sop(s4.compareTo(s5)); 27. } 28. public static void method_sub() 29. { 30. String s = "abcdeadf"; 31. String s1 = s.substring(3); 32. String s2 = s.substring(2,4); 33. sop(s1); 34. sop(s2); 35. } 36. public static void method_split() 37. { 38. String s = "hubiao,liuyang,bendan"; 39. String[] arr = s.split(","); 40. for (int x = 0;x 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