Java字符串格式方法大全

实现思路：
    我们可以使用String.format对输入的字符串进行格式化

转换的通配符

String.format示例分享

package com.java265;
public class JavaStringFormat1 {
    public static void main(String[] args) {
        String result = String.format("%s is %d", "java265", 18);     // java265 is 18
        System.out.println(result);
 
        String result2 = String.format("%d + %d = %d", 1, 2, 1 + 2); // 1 + 2 = 3
        System.out.println(result2);
 
        String result3 = String.format("%s = %f", "PI", Math.PI);    // PI = 3.141593
        String result4 = String.format("%s = %.3f", "PI", Math.PI);  // PI = 3.142
        System.out.println(result3);
        System.out.println(result4);
    }
}

重新排列参数信息

使用%{index}${conversion}
  %1$ –第一个参数
  %2$ –第二个参数
  %3$ –第三个参数
  %{index}$ – {index}参数

package com.java265;
 
public class JavaStringFormat2 {
 
    public static void main(String[] args) {
 
        String a1 = "java1";
        String a2 = "java2";
        Integer a3 = 888;
 
        String result = String.format("Test: %3$d, %1$s, %1$s, %2$s", a1, a2, a3);
 
        System.out.println(result);
    }
}

------运行以上代码,将输出以下信息-----
Test: 888, java1, java1, java2

字符串占位符示例分享

package com.java265;
public class JavaStringFormat3 {
    public static void main(String[] args) {
        String input = "Hello World";
        // default
        String result1 = String.format("|%s|", input);              // |Hello World|
 
        // this %s has length of 20, format as %20s, pad 20 characters
        // default right-justified
        String result2 = String.format("|%20s|", "Hello World");    // |         Hello World|
 
        // left-justified
        String result3 = String.format("|%-20s|", "Hello World");   // |Hello World         |
 
        // max length = 5
        String result4 = String.format("|%.5s|", "Hello World");    // |Hello|
 
        // left pad with $
        String result5 = String.format("|%20s|", "Hello World")     // |$$$$$$$$$Hello$World|
                .replace(' ', '$');
 
        // left pad with $, ignore spaces in string
        String result6 = padLeft("Hello World", 20, "$");          // $$$$$$$$$Hello World
 
        System.out.println(result1);
        System.out.println(result2);
        System.out.println(result3);
        System.out.println(result4);
        System.out.println(result5);
        System.out.println(result6);
    }
 
    public static String padLeft(String str, int width, String padWith) {
        String result = "";
        String temp = String.format("%" + width + "s", str);
        if (temp.length() > str.length()) {
            result = temp.substring(0, temp.length() - str.length()).replace(" ", padWith);
        }
        result += str;
        return result;
    }
}

----运行以上代码,将输出以下信息----

|Hello World|
|         Hello World|
|Hello World         |
|Hello|
|$$$$$$$$$Hello$World|
$$$$$$$$$Hello World

String.format输出整数

package com.java265;
 
public class JavaStringFormat4 {
 
    public static void main(String[] args) {
 
        // default
        String result1 = String.format("|%d|", 100);                // |100|
 
        // this %d has length of 20, format as %20d, pad 20 characters
        // default right-justified
        String result2 = String.format("|%20d|", 100);              // |                 100|
 
        // left-justified
        String result3 = String.format("|%-20d|", 100);             // |100                 |
 
        // left pad with 0
        String result4 = String.format("|%020d|", 100);             // |00000000000000000100|
 
        // prefix with +
        String result5 = String.format("|%+20d|", 100);             // |                +100|
 
        // negative
        String result6 = String.format("|%20d|", -100);             // |                -100|
 
        // octal
        String result7 = String.format("|%20o|", 100);              // |                 144|
 
        // hex
        String result8 = String.format("|%20x|", 30);               // |                  1e|
 
        // prefix 0x with #
        String result9 = String.format("|%#20x|", 30);              // |                0x1e|
 
        System.out.println(result1);
        System.out.println(result2);
        System.out.println(result3);
        System.out.println(result4);
        System.out.println(result5);
        System.out.println(result6);
        System.out.println(result7);
        System.out.println(result8);
        System.out.println(result9);
 
    }
 
}

------运行以上代码，将输出以下信息-----
|100|
|                 100|
|100                 |
|00000000000000000100|
|                +100|
|                -100|
|                 144|
|                  1e|
|                0x1e|

String.format输出浮点数

package com.java265;
 
public class JavaStringFormat5 {
 
    public static void main(String[] args) {
 
        double pi = Math.PI;
 
        // default
        String result1 = String.format("%f", pi);       // 3.141593
 
        // 2 decimal points
        String result2 = String.format("%.2f", pi);     // 3.14
 
        String result3 = String.format("%e", pi);       // 3.141593e+00
 
        String result4 = String.format("%a", pi);       // 0x1.921fb54442d18p1
 
        // right
        String result5 = String.format("|%20f|", pi);   // |            3.141593|
 
        // left
        String result6 = String.format("|%-20f|", pi);  // |3.141593            |
 
        System.out.println(result1);
        System.out.println(result2);
        System.out.println(result3);
        System.out.println(result4);
        System.out.println(result5);
        System.out.println(result6);
 
    }
 
}

-----运行以上代码,将输出以下信息-----
3.141593
3.14
3.141593e+00
0x1.921fb54442d18p1
|            3.141593|
|3.141593            |

String.format注意事项:
    当左边需使用0进行补充时
	可使用String.format实现，如下例所示
	// 1100100
  String result1 = String.format("%s", Integer.toBinaryString(100));
 
  // 00000000000000000000000001100100
  String result2 = String.format("%32s", Integer.toBinaryString(100)).replace(" ", "0");
 
  // 00000000000000011110001001000000
  String result3 = String.format("%32s", Integer.toBinaryString(123456)).replace(" ", "0");