Common methods of Java foundation _0308:string class

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Remove the character of the specified index--using the Charat () method
public class StringDemo {    public static void main(String args[]) {        String str = "hello";       // 定义字符串对象        char c = str.charAt(0);     // 截取第一个字符        System.out.println(c);      // 输出字符    }}程序执行结果:h
Conversion of character arrays to strings
public class StringDemo {    public static void main(String args[]) {        String str = "hello";       // 定义字符串        char[] data = str.toCharArray(); // 将字符串变为字符数组        for (int x = 0; x < data.length; x++) { // 循环输出每一个字符            System.out.print(data[x] + "、");        }    }}程序执行结果: h、e、l、l、o、
Turn a string to uppercase
public class StringDemo {    public static void main(String args[]) {        String str = "hello“;       // 字符串由小写字母组成        char[] data = str.toCharArray();    // 将字符串变为字符数组        for (int x = 0; x < data.length; x++) { // 改变每一个字符的编码值            data[x] -= 32;        }        System.out.println(new String(data));   // 将全部字符数组变为String        System.out.println(new String(data, 1, 2)); // 将部分字符数组变为String    }}程序执行结果:HELLOEL
Given a string, it is required to determine whether it is made up of numbers.
public class StringDemo {    public static void main(String args[]) {        String str = "123423432";        if (isNumber(str)) {            System.out.println("字符串由数字组成!");        } else {            System.out.println("字符串由非数字组成!");        }    }    public static boolean isNumber(String temp) {        char[] data = temp.toCharArray();// 将字符串变为字符数组,可以取出每一位字符进行判断        for (int x = 0; x < data.length; x++) {// 循环判断            if (data[x] > ‘9‘ || data[x] < ‘0‘) {// 不是数字字符范围                return false;// 后续不再判断            }        }        return true;    // 如果全部验证通过返回true    }}程序执行结果: 字符串由数字组成!
To observe the conversion of a string to a byte array
public class StringDemo {    public static void main(String args[]) {        String str = "helloworld";  // 定义字符串        byte[] data = str.getBytes();   // 将字符串变为字节数组        for (int x = 0; x < data.length; x++) {            data[x] -= 32;  // 将小写字母变为大写形式        }        System.out.println(new String(data)); // 全部转换        System.out.println(new String(data, 5, 5));// 部分转换    }}程序执行结果:HELLOWORLD(“new String(data)”语句执行结果)WORLD(“new String(data, 5, 5)”语句执行结果)
Equal judgment
public class StringDemo {    public static void main(String args[]) {        String stra = "Hello"; // 实例化字符串对象        String strb = "hELLO"; // 实例化字符串对象        System.out.println(stra.equals(strb));  // 比较结果:false        System.out.println(stra.equalsIgnoreCase(strb));  // 比较结果:true    }}程序执行结果:false(“stra.equals(strb)”语句执行结果)true(“stra.equalsIgnoreCase(strb)”语句执行结果)
Observe the CompareTo () method
public class StringDemo {    public static void main(String args[]) {        String stra = "Hello";  // 定义字符串对象        String strb = "HEllo";  // 定义字符串对象        System.out.println(stra.compareTo(strb)); // 32,大于0        if (stra.compareTo(strb) > 0) {// 可以利用大小等于0的方式来判断大小            System.out.println("大于");        }    }}程序执行结果:32(“stra.compareTo(strb)”语句执行结果,比较的是两个字符串的编码数值)大于(“System.out.println("大于");”语句执行结果)
Use features such as indexof () to find
public class StringDemo {    public static void main(String args[]) {        String str = "helloworld";      // 实例化字符串对象        System.out.println(str.indexOf("world"));   // 返回满足条件单词的第一个字母的索引        System.out.println(str.indexOf("l"));   // 返回的是第一个查找到的子字符串位置        System.out.println(str.indexOf("l", 5));    // 从第6个元素开始查找子字符串位置        System.out.println(str.lastIndexOf("l"));   // 从后开始查找指定字符串的位置    }}程序执行结果:5(“System.out.println(str.indexOf("world"));”语句执行结果)2(“System.out.println(str.indexOf("l"));”语句执行结果)8(“System.out.println(str.indexOf("l", 5));”语句执行结果)8(“System.out.println(str.lastIndexOf("l"));”语句执行结果)
Use the IndexOf () method to determine if the substring exists
public class StringDemo {    public static void main(String args[]) {        String str = "helloworld“;  // 字符串对象        if (str.indexOf("world") != -1) { // 能找到子字符串            System.out.println("可以查询到数据。");        }    }}程序执行结果:可以查询到数据。
Use the contains () method to determine if the substring exists
public class StringDemo {    public static void main(String args[]) {        String str = "helloworld“;      // 字符串对象        if (str.contains("world")) {    // 子字符串存在            System.out.println("可以查询到数据。");        }    }}程序执行结果: 可以查询到数据。
Start or end judgment
public class StringDemo {    public static void main(String args[]) {        String str = "##@@hello**";     // 字符串对象        System.out.println(str.startsWith("##"));// 是否以“##”开头        System.out.println(str.startsWith("@@", 2));    // 从第2个索引开始是否以“@@”开头        System.out.println(str.endsWith("**"));// 是否以“**”结尾    }}程序执行结果:true(“str.startsWith("##")”语句执行结果)true(“str.startsWith("@@", 2)”语句执行结果)true(“str.endsWith("**")”语句执行结果)
Example: Observing the result of the substitution
public class StringDemo {    public static void main(String args[]) {        String str = "helloworld" ;         // 定义字符串        String resultA = str.replaceAll("l","_") ;  // 全部替换        String resultB = str.replaceFirst("l","_") ;    // 替换首个        System.out.println(resultA) ;        System.out.println(resultB) ;    }}程序执行结果:he__owor_d(“System.out.println(resultA)”语句执行结果)he_loworld(“System.out.println(resultB)”语句执行结果)
Validating string Operations
public class StringDemo {    public static void main(String args[]) {        String str = "helloworld";      // 定义字符串        String resultA = str.substring(5);  // 从指定索引截取到结尾        String resultB = str.substring(0, 5);   // 截取部分子字符串        System.out.println(resultA);        System.out.println(resultB);    }}程序执行结果:world(“System.out.println(resultA)”语句执行结果)hello(“System.out.println(resultB)”语句执行结果)
Do all of the splitting
public class StringDemo {    public static void main(String args[]) {        String str = "hello yootk nihao mldn";// 定义字符串,中间使用空格作为间隔        String result[] = str.split(" ");   // 字符串拆分        for (int x = 0; x < result.length; x++) {   // 循环输出            System.out.print(result[x] + "、");        }    }}程序执行结果:hello、yootk、nihao、mldn、
Split into a specified number
public class StringDemo {    public static void main(String args[]) {        String str = "hello yootk nihao mldn";  // 定义字符串,中间使用空格作为间隔        String result[] = str.split(" ",2);     // 字符串拆分        for (int x = 0; x < result.length; x++) {   // 循环输出            System.out.println(result[x]);        }    }}程序执行结果:helloyootk nihao mldn
Complex split
public class StringDemo {    public static void main(String args[]) {        String str = "张三:20|李四:21|王五:22“;// 定义字符串        String result[] = str.split("\\|"); // 第一次拆分        for (int x = 0; x < result.length; x++) {            String temp[] = result[x].split(":");   // 第二次拆分            System.out.println("姓名:" + temp[0] + ",年龄:" + temp[1]);        }    }}程序执行结果:姓名:张三,年龄:20姓名:李四,年龄:21姓名:王五,年龄:22
String connection
public class StringDemo {    public static void main(String args[]) {        String str = "hello".concat("world") ;  // 等价于“+”        System.out.println(str) ;    }}程序执行结果:helloworld
Example: Turn lowercase and uppercase operations
public class StringDemo {    public static void main(String args[]) {        String str = "(*(*Hello(*(*" ;      // 定义字符串        System.out.println(str.toUpperCase()) ; // 转大写后输出        System.out.println(str.toLowerCase()) ; // 转小写后输出    }}程序执行结果:(*(*HELLO(*(*(“System.out.println(str.toUpperCase())”语句执行结果)(*(*hello(*(*(“System.out.println(str.toLowerCase())”语句执行结果)
Remove left and right spaces
public class StringDemo {    public static void main(String args[]) {        String str = "   hello   world  ";  // 定义字符串,包含空格        System.out.println("【" + str + "】");// 原始字符串        System.out.println("【" + str.trim() + "】");// 去掉空格后的字符串,中间的空格保留    }}程序执行结果:【   hello   world  】【hello   world】
Get string length
public class StringDemo {    public static void main(String args[]) {        String str = "helloworld";  // 定义字符串        System.out.println(str.length());// 取得字符串长度    }}程序执行结果:10
Example: determining whether an empty string
public class StringDemo {    public static void main(String args[]) {        String str = "helloworld";      // 定义字符串        System.out.println(str.isEmpty());  // 判断字符串对象的内容是否为空字符串(不是null)        System.out.println("".isEmpty());    // 判断字符串常量的内容是否为空字符串(不是null)    }}程序执行结果:false(“System.out.println(str.isEmpty())”语句执行结果)true(“System.out.println("".isEmpty())”语句执行结果)
To implement the first letter capitalization operation
public class StringDemo {    public static void main(String args[]) {        String str = "yootk";   // 定义字符串        System.out.println(initcap(str));// 调用initcap()方法    }    /**     * 实现首字母大写的操作     * @param temp 要转换的字符串数据     * @return 将首字母大写后返回     */    public static String initcap(String temp) {        // 利用substring(0,1)取出字符串的第一位而后将其大写,再连接剩余的字符串        return temp.substring(0, 1).toUpperCase() + temp.substring(1);    }}程序执行结果:Yootk

Common methods of Java foundation _0308:string class

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