java 格式化

Posted 2021-02-05 飞龙dragon

 一. 可以之际像c语言一样用System.out.printf()格式化输出

二. System.out.format

1. format()方法模仿自printf(), 可用于PrintStream或PrintWrter对象,其中也包括System.out对象

三.Formatter类

1.在java中所有新的格式化功能都由java.util.Formatter类处理,可以将Formatter看做是一个翻译器,它将你的格式化字符串与数据翻译成需要的结果,formatter的构造器器经过重载可以接受多种输出的目的地

package strings;
//: strings/Turtle.java
import java.io.*;
import java.util.*;

public class Turtle {
  private String name;
  private Formatter f;
  public Turtle(String name, Formatter f) {
    this.name = name;
    this.f = f;
  }
  public void move(int x, int y) {
    f.format("%s The Turtle is at (%d,%d)\\n", name, x, y);
  }
  public static void main(String[] args) {
    PrintStream outAlias = System.out;
    Turtle tommy = new Turtle("Tommy", //所有的tommy都将输出到System.out
      new Formatter(System.out));
    Turtle terry = new Turtle("Terry", //所有的Terry都将输出到System.out一个别名中, 这种最常用
      new Formatter(outAlias));
    tommy.move(0,0);
    terry.move(4,8);
    tommy.move(3,4);
    terry.move(2,5);
    tommy.move(3,3);
    terry.move(3,3);
  }
} /* Output:
Tommy The Turtle is at (0,0)
Terry The Turtle is at (4,8)
Tommy The Turtle is at (3,4)
Terry The Turtle is at (2,5)
Tommy The Turtle is at (3,3)
Terry The Turtle is at (3,3)
*///:~

2. 格式化说明符

 Formatter类格式化抽象语法: %[argument_index][flags][width][.precision]conversion

• 用"-"标志来改变对齐方向(默认右对齐),添加了"-"表示左对齐
• argument_index控制输出顺序  当有多个参数要输出时(比如format("s: %2$s %s\\n", "sdffads","fds");)输出结果为s: fds sdffads
• width: 控制一个域的最小尺寸,
• flags 
• precision(精度): 用来指明最大尺寸,用于String时,它表示打印String时输出字符的最大数量.用于浮点数时,表示小数显示的位数(默认6位),小数过多则舍入,过少则在尾部补零.用于整数时,会出发异常.

1. public final class Locale extends Object  
2.     Locale 对象表示了特定的地理、政治和文化地区  
3. 字段摘要  
4.     Locale.CHINA   
5.           用于表示中国常量  
6.     Locale.US   
7.           用于表示美国常量  
8.     Locale.JAPAN   
9.           用于表示日本常量  
10. 使用方法: String.format(Locale.US,"i = %d, l = %d, f = %f, d = %f",i,l,f,d);

2.如果需要用变量统一控制格式化宽度可以使用下面的方法

package strings;

import java.util.*;

class Receipt {
    public static final int ITEM_WIDTH = 15;
    public static final int QTY_WIDTH = 5;
    public static final int PRICE_WIDTH = 10;
    private static final String TITLE_FRMT = "%-" + ITEM_WIDTH + "s %" + QTY_WIDTH + "s %" + PRICE_WIDTH + "s\\n";
    private static final String ITEM_FRMT = "%-" + ITEM_WIDTH + "." + ITEM_WIDTH + "s %" + QTY_WIDTH + "d %"
            + PRICE_WIDTH + ".2f\\n";
    private static final String TOTAL_FRMT = "%-" + ITEM_WIDTH + "s %" + QTY_WIDTH + "s %" + PRICE_WIDTH + ".2f\\n";
    private double total = 0;
    Formatter f = new Formatter(System.out, Locale.US);

    public void printTitle() {
        f.format(TITLE_FRMT, "Item", "Qty", "Price");
        f.format(TITLE_FRMT, "----", "---", "-----");
    }

    public void print(String name, int qty, double price) {
        f.format(ITEM_FRMT, name, qty, price);
        total += price;
    }

    public void printTotal() {
        f.format(TOTAL_FRMT, "Tax", "", total * 0.06);
        f.format(TITLE_FRMT, "", "", "-----");
        f.format(TOTAL_FRMT, "Total", "", total * 1.06);
    }
}

public class E04_CustomizableReceipt {
    public static void main(String[] args) {
        Receipt receipt = new Receipt();
        receipt.printTitle();
        receipt.print("Jack\'s Magic Beans", 4, 4.25);
        receipt.print("Princess Peas", 3, 5.1);
        receipt.print("Three Bears Porridge", 1, 14.29);
        receipt.printTotal();
    }
}

四. String.format()

•  String.format()是一个static方法,接受与Formatter.format()方法一样的参数,但返回一个String对象.
• String.format()内部,它也是创建一个Formatter对象,然后将你传入的参数转给Formatter.

package strings;
//: strings/DatabaseException.java

public class DatabaseException extends Exception {
  public DatabaseException(int transactionID, int queryID,
    String message) {
    super(String.format("(t%d, q%d) %s", transactionID,
        queryID, message));
  }
  public static void main(String[] args) {
    try {
      throw new DatabaseException(3, 7, "Write failed");
    } catch(Exception e) {
      System.out.println(e);
    }
  }
} /* Output:
DatabaseException: (t3, q7) Write failed
*///:~

五. 一个十六进制转储(dump)工具

//: net/mindview/util/Hex.java
package object;
import java.io.*;

public class Hex {
  public static String format(byte[] data) {
    StringBuilder result = new StringBuilder();
    int n = 0;
    for(byte b : data) {
      if(n % 16 == 0)
        result.append(String.format("%05X: ", n));
      result.append(String.format("%02X ", b));
      n++;
      if(n % 16 == 0) result.append("\\n");
    }
    result.append("\\n");
    return result.toString();
  }
  public static void main(String[] args) throws Exception {
    if(args.length == 0)
      // Test by displaying this class file:
      System.out.println(
        format(BinaryFile.read("bin/object/Hex.class")));
    else
      System.out.println(
        format(BinaryFile.read(new File(args[0]))));
  }
} /* Output: (Sample)
00000: CA FE BA BE 00 00 00 31 00 52 0A 00 05 00 22 07
00010: 00 23 0A 00 02 00 22 08 00 24 07 00 25 0A 00 26
00020: 00 27 0A 00 28 00 29 0A 00 02 00 2A 08 00 2B 0A
00030: 00 2C 00 2D 08 00 2E 0A 00 02 00 2F 09 00 30 00
00040: 31 08 00 32 0A 00 33 00 34 0A 00 15 00 35 0A 00
00050: 36 00 37 07 00 38 0A 00 12 00 39 0A 00 33 00 3A
...
*///:~
//: net/mindview/util/BinaryFile.java
// Utility for reading files in binary form.
package object;
import java.io.*;

public class BinaryFile {
  public static byte[] read(File bFile) throws IOException{
    BufferedInputStream bf = new BufferedInputStream(
      new FileInputStream(bFile));
    try {
      byte[] data = new byte[bf.available()];
      bf.read(data);
      return data;
    } finally {
      bf.close();
    }
  }
  public static byte[]
  read(String bFile) throws IOException {
    return read(new File(bFile).getAbsoluteFile());
  }
} ///:~

 六.最全的示例

package strings;

import java.math.*;
import java.util.*;
import static net.mindview.util.Print.*;

public class E05_ComplexConversion {
    public static void main(String[] args) {
        Formatter f = new Formatter(System.out, Locale.US);

        char u = \'a\';
        print("u = \'a\'");
        f.format("s: %1$-10s\\n", u);
        f.format("c: %1$-10c\\n", u);
        f.format("b: %1$-10.10b\\n", u);
        f.format("h: %1$-10.10h\\n", u);
        int v = 1000;
        print("v = 1000");
        f.format("d 1: %1$(,0+10d\\n", v);
        f.format("d 2: %1$-(, 10d\\n", v);
        f.format("d 3, v = -v: %1$-(, 10d\\n", -v);
        f.format("c, v = 121: %1$-10c\\n", 121);
        f.format("b: %1$-10.10b\\n", v);
        f.format("s: %1$-10.10s\\n", v);
        f.format("x: %1$-10x\\n", v);
        f.format("h: %1$-10.10h\\n", v);
        BigInteger w = new BigInteger("50000000000000");
        print("w = new BigInteger(\\"50000000000000\\")");
        f.format("d 1: %1$(,0+10d\\n", w);
        f.format("d 2: %1$-(, 10d\\n", w);
        f.format("d 3, w = -w: %1$-(, 10d\\n", w.negate());
        f.format("b: %1$-10.10b\\n", w);
        f.format("s: %1$-10.10s\\n", w);
        f.format("x 1: %1$(0+10x\\n", w);
        f.format("x 2: %1$-( 10x\\n", w);
        f.format("x 3, w = -w: %1$-( 10x\\n", w.negate());
        f.format("h: %1$-10.10h\\n", w);
        double x = 179.543;
        print("x = 179.543");
        f.format("b: %1$-10.10b\\n", x);
        f.format("s: %1$-10.10s\\n", x);
        f.format("f 1: %1$#(,0+10.2f\\n", x);
        f.format("f 2: %1$#(,- 10.2f\\n", x);
        f.format("f 3, x = -x: %1$#(,0+10.2f\\n", -x);
        f.format("e 1: %1$#(0+10.2e\\n", x);
        f.format("e 2: %1$#(- 10.2e\\n", x);
        f.format("e 3, x = -x: %1$#(0+10.2e\\n", -x);
        f.format("h: %1$-10.10h\\n", x);
        Object y = new Object();
        print("y = new Object()");
        f.format("b: %1$-10.10b\\n", y);
        f.format("s: %1$-10.10s\\n", y);
        f.format("h: %1$-10.10h\\n", y);
        boolean z = false;
        print("z = false");
        f.format("b: %1$-10.10b\\n", z);
        f.format("s: %1$-10.10s\\n", z);

        f.format("h: %1$-10.10h\\n", z);
    }
}/*

u = \'a\'
s: a
c: a
b: true
h: 61
v = 1000
d 1: +00001,000
d 2: 1,000
d 3, v = -v: (1,000)
c, v = 121: y
b: true
s: 1000
x: 3e8
h: 3e8
w = new BigInteger("50000000000000")
d 1: +50,000,000,000,000
d 2: 50,000,000,000,000
d 3, w = -w: (50,000,000,000,000)
b: true
s: 5000000000
x 1: +2d79883d2000
x 2: 2d79883d2000
x 3, w = -w: (2d79883d2000)
h: 8842a1a7
x = 179.543
b: true
s: 179.543
f 1: +000179.54
f 2: 179.54
f 3, x = -x: (00179.54)
e 1: +01.80e+02
e 2: 1.80e+02
e 3, x = -x: (1.80e+02)
h: 1ef462c
y = new Object()
b: true
s: java.lang.
h: 6d06d69c
z = false
b: false
s: false
h: 4d5

*/