Question

我是Java新手，正在尝试学习地图的概念。

我想出了下面的代码。但是，我想同时打印出“key String”和“value String”。

ProcessBuilder pb1 = new ProcessBuilder();
Map<String, String> mss1 = pb1.environment();
System.out.println(mss1.size());

for (String key: mss1.keySet()){
    System.out.println(key);
}

我只能找到只打印“键字符串”的方法。

Answer 1

有多种方法可以实现这一目标。这是三个。

    Map<String, String> map = new HashMap<String, String>();
    map.put("key1", "value1");
    map.put("key2", "value2");
    map.put("key3", "value3");

    System.out.println("using entrySet and toString");
    for (Entry<String, String> entry : map.entrySet()) {
        System.out.println(entry);
    }
    System.out.println();

    System.out.println("using entrySet and manual string creation");
    for (Entry<String, String> entry : map.entrySet()) {
        System.out.println(entry.getKey() + "=" + entry.getValue());
    }
    System.out.println();

    System.out.println("using keySet");
    for (String key : map.keySet()) {
        System.out.println(key + "=" + map.get(key));
    }
    System.out.println();

输出

using entrySet and toString
key1=value1
key2=value2
key3=value3

using entrySet and manual string creation
key1=value1
key2=value2
key3=value3

using keySet
key1=value1
key2=value2
key3=value3

Answer 2

在循环内部，您有密钥，您可以使用该密钥从Map中检索值：

for (String key: mss1.keySet()) {
    System.out.println(key + ": " + mss1.get(key));
}

Answer 3

col1 <- c('1/2 in. x 1/2 in. x 3/4 ft. Copper Pressure Cup', 'Ensemble 60 in. x 43-1/2 in. x 54-1/4 in. 3-piece',
'2-3/4 in. x 4-1/2 in. Heavy-Duty',
'1/4-20 x 2 in. Forged Steel ',
'1/2-Amp Slo-Blo GMA Fuse',
'3/4 in. x 12 in. x 24 in. White Thermally',
'12.0 oz. of weight',
'1.4 fl. oz. of liquid',
'14 gal. tall',
'Sahara Wood 47 in. Long x 12-1/8 in. Deep x 1-11/16 in. Height',
'1/25 HP Cast Iron ',
'1/2 in., 3/4 in. and 1 in. PVC ',
'24-3/4 in. x 48-3/4 in. x 1-1/4 in. Faux Windsor',
'8 oz. -200 Pot Of Cream',
'5/8 in. dia. x 25 ft. Water ',
'18.5 / 30.5 in. Brushed Nickel',
'57-1/2 in. x 70-5/16 in. Semi-Framed',
'2-1/4 HP Router',
'12-Volt Lithium-Ion Cordless 3/8 in.',
'12-Gauge 24-5/8 in. Strap ',
'7-3/4 in. Wigan Ceiling',
'1 qt. B-I-N ',
'3/8 in. O.D. x 1/4 in. NPTF',
'2-1/2 in. Long x 5/8 in. Diameter Spring',
'1/4 x 3 in. Heat-Shrink ',
'4-White PVC End',
'41000 Series Non-Vented Range',
'Revival 1-Spray 5-Katalyst Air',
'180-Degree White Outdoor',
'3/8 x 3 Hand Scraped ',
'67-Qt. Jug',
'35-77-7/8 in. White',
'-16 tpi x 4 in. Stainless Steel',
'3-21 degree Full')

df <- data.frame(col1 = col1)

df
                                                             col1
1                 1/2 in. x 1/2 in. x 3/4 ft. Copper Pressure Cup
2               Ensemble 60 in. x 43-1/2 in. x 54-1/4 in. 3-piece
3                                2-3/4 in. x 4-1/2 in. Heavy-Duty
4                                    1/4-20 x 2 in. Forged Steel 
5                                        1/2-Amp Slo-Blo GMA Fuse
6                       3/4 in. x 12 in. x 24 in. White Thermally
7                                              12.0 oz. of weight
8                                           1.4 fl. oz. of liquid
9                                                    14 gal. tall
10 Sahara Wood 47 in. Long x 12-1/8 in. Deep x 1-11/16 in. Height
11                                             1/25 HP Cast Iron 
12                                1/2 in., 3/4 in. and 1 in. PVC 
13               24-3/4 in. x 48-3/4 in. x 1-1/4 in. Faux Windsor
14                                        8 oz. -200 Pot Of Cream
15                                   5/8 in. dia. x 25 ft. Water 
16                                 18.5 / 30.5 in. Brushed Nickel
17                           57-1/2 in. x 70-5/16 in. Semi-Framed
18                                                2-1/4 HP Router
19                           12-Volt Lithium-Ion Cordless 3/8 in.
20                                     12-Gauge 24-5/8 in. Strap 
21                                        7-3/4 in. Wigan Ceiling
22                                                   1 qt. B-I-N 
23                                    3/8 in. O.D. x 1/4 in. NPTF
24                       2-1/2 in. Long x 5/8 in. Diameter Spring
25                                       1/4 x 3 in. Heat-Shrink 
26                                                4-White PVC End
27                                  41000 Series Non-Vented Range
28                                 Revival 1-Spray 5-Katalyst Air
29                                       180-Degree White Outdoor
30                                          3/8 x 3 Hand Scraped 
31                                                     67-Qt. Jug
32                                            35-77-7/8 in. White
33                                -16 tpi x 4 in. Stainless Steel
34                                               3-21 degree Full

Map <string，string =“”>，如何同时打印“键字符串”和“值字符串”

3 个答案:

输出