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{% code %} package _22javacoreclass;

public class Main{ public static void main(String[] args){ String s1 = "hello"; String s2 = "HELLO"; String s3 = new String(new char[]{'h','e','l','l','o'}); String s4 = s1.toUpperCase();

    // 1.字符串比较
    System.out.println(s1.equals(s4));                // false
    // 2.忽略大小写比较
    System.out.println(s1.equalsIgnoreCase(s2));      // true
    // 3.是否包含子串
    System.out.println("Hello".contains("ll"));       // true
    // 4.返回第一个匹配字符的索引
    System.out.println("Hello".indexOf("l"));         // 2
    // 5.返回最后一个匹配字符的索引
    System.out.println("Hello".lastIndexOf("l"));     // 3
    // 6.是否以指定字符串前缀开始
    System.out.println("Hello".startsWith("He"));     // true
    // 7.是否以指定字符串结尾
    System.out.println("Hello".endsWith("lo"));       // true
    // 8.提取2到结尾子串
    System.out.println("Hello".substring(2));         //"llo"
    // 9.提取2到3子串
    System.out.println("Hello".substring(2, 4));      //"ll"
    // 10.去除收尾空白字符
    System.out.println("  \tHello\r\n ".trim());      // "Hello"
    // 11.去空格     java11以后特性
    // System.out.println("\u3000Hello\u3000".strip());  // "Hello"
    // 12.去前缀空格 java11以后特性
    // System.out.println(" Hello ".stripLeading());     // "Hello "
    // 13.去结尾空格  java11以后特性
    // System.out.println(" Hello ".stripTrailing());    // " Hello"
    // 14.判断字符串是否为空
    System.out.println("".isEmpty());                 //true
    System.out.println("  ".isEmpty());               //false
    // 15.判断字符串是否包含空白字符串 java11以后特性
    // System.out.println("  \n".isBlank());             //true
    // System.out.println(" Hello ".isBlank());          //false
    // 16.替换子串
    System.out.println("hello".replace('l','w'));                     // hewwo
    // 17.表达式替换
    System.out.println("A,,B;C ,D".replaceAll("[\\,\\;\\s]+", ",")); // A,B,C,D
    // 18.分割字符串
    System.out.println("A,B,C,D".split("\\,"));             // {"A","B","C","D"}
    // 19.拼接字符串
    String[] arr = {"A", "B", "C"};
    System.out.println(String.join("***",arr));             //A***B***C
    // 20.类型转换为字符串
    System.out.println(String.valueOf(123));                // "123"
    System.out.println(String.valueOf(45.67));              // "45.67"
    System.out.println(String.valueOf(true));               // "true"
    System.out.println(String.valueOf(new Object()));       //类似java.lang.Object@4554617c
    // 21.字符串转换为int
    System.out.println(Integer.parseInt("123"));         //123
    System.out.println(Integer.parseInt("ff",16));       //按十六进制转换, 255
    // 22.字符串转换为boolean
    System.out.println(Boolean.parseBoolean("true"));    //true
    System.out.println(Boolean.parseBoolean("FASLE"));   //false
    // 23.转换为char[]
    char[] cs = "Hello".toCharArray();
    System.out.println(cs);                    //String转char[], Hello
    System.out.println(new String(cs));        //char[]转String, Hello
}

} {% endcode %}