Last time there was a little bit of the string class that was not completely covered, that is, it was about the string builder.

One.string builder

To continuously increase the content of a string object in Java can be achieved by continuously creating a new string object using the splicing character "+". as follows:

	        String str1="abc";
		String str2="def";
		str1+=str2;
		System.out.println(str1);

But there is a disadvantage of this, that is, every splicing needs to construct a new string object, which wastes space and time. Then the StringBuilder class in Java solves this problem. The code is as follows:

        StringBuilder strb=new StringBuilder();
	strb.append("asdas");
	strb.append("asdasd");
	String str=strb.toString();
	System.out.println(str);

Two main methods: append() adds a string to the builder, and tostring is converted to a string object.

2. Input and output

The input must first define a Scanner object and associate System.in. Import the package Java.util;

There are more methods for the Scanner class, mainly the following:

nextline() reads a line, this is mainly to read the spaces in a line. If you want to read a word, use the next() method. code show as below:

        Scanner scan=new Scanner(System.in);
	System.out.println("Read a line including spaces!");
	String str1=scan.nextLine();
	 System.out.println("Read a word separated by a space!");
	String str2=scan.next();
	System.out.println(str1);
	System.out.println(str2);

result:

Formatted output:

The printf() function of c is quoted in Java, and the output format is specified by interspersing quotation marks%.

Conversion characters for common printf:

d Decimal number x Hexadecimal number o Octal number f Fixed-point floating-point number e Exponential output floating-point number g Universal floating-point number a Hexadecimal number% s string number as follows c

	System.out.printf("%o",20);
	System.out.printf("%s", "asdafa");

Other conversion symbols:

+When printing positive and negative signs

Add a space before the positive number

-Left aligned

code show as below:

System.out.printf("%-8.6f",6.012);

The format is: "(starting character)% (whether it contains)-(left-aligned if it contains) Format mn (m represents the output length, n represents the number of digits after the decimal point) (letters) f, l, etc. to output the value Modification of form".

The syntax diagram is as follows: