String,StringBuilder的方法,伪随机Random类

import java.nio.charset.Charset;

public class StringDemo {
    public static void main(String[] args) {
        byte[]bt={‘a‘,‘b‘,‘c‘};
//        String(byte[]bt,Charset charset);
//        该构造方法根据给定的byte数组和字符集组成一个新的String对象
        Charset charset=Charset.forName("utf-8");
        String s1=new String(bt,charset);
        System.out.println(s1);
        System.out.println(s1.charAt(1));
        String s2="abcde";
//        s2的前半部分是s1,compareTo方法返回两个字符串的长度差
        System.out.println(s1.compareTo(s2));
//        s1,s3从0(a)开始比较,返回第一个不相等的字符差(b与a之差)
        String s3="aac";
        System.out.println(s1.compareTo(s3));
//        concat字符串连接,与+作用相同
        System.out.println(s1.concat(s2));
        System.out.println(s1.concat(s2).endsWith(s2));
        System.out.println(s1.equalsIgnoreCase("ABC"));
        byte[]bb=s1.getBytes();
        char []ch=new char[s1.length()-1];
        System.out.println((char)bb[1]);
        s1.getChars(0, s1.length()-1,ch, 0);
        System.out.println(s1.replace(‘a‘, ‘A‘));
        System.out.println(s1);
    }

}

StringBuilder

public class BuilderDemo {
    public static void main(String[] args) {
        StringBuilder sb=new StringBuilder();
        sb.append(" here ");
        sb.append("am ");
        sb.append("I ");
        System.out.println(sb);
        sb.insert(5," here");
        System.out.println(sb);
        System.out.println(sb.reverse());
        sb.delete(2,3);
        sb.setLength(5);
        System.out.println(sb.length());
        System.out.println(sb.capacity());
    }
}

public class RandDemo {
    public static void main(String[] args) {
        Random rand=new Random(100);
        System.out.println(rand.nextBoolean());
        System.out.println(rand.nextInt());
        Random rand2=new Random(100);
//        rand2 rand的运行结果一样
        System.out.println(rand2.nextInt());
        System.out.println(rand2.nextBoolean());

    }

}

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