Java Misc.

[xiedaxia1hao]

Random Java Language Syntax and so on.

[xiedaxia1hao]

Map Iteration

Map<Integer, Integer> map = new HashMap<>();

// Iterate by Entry
for(Map.Entry<Integer, Integer> entry : map.entrySet()) {
  int key = entry.getKey();
  int value = entry.getValue();
  // do your stuff 
}

// Iterate by Key Set
for(Integer key : map.keySet()) {
  int random = key + map.get(key);
  // do your stuff
} 

// Iterate by Value Set
for(Integer value : map.values()) {
  int random = value + 100;
  // do your stuff
} 

[xiedaxia1hao]

Regex

• String Split by Space

  // the first \ is used to escape the second \ 
  // \s represents a whitespace character including [ \t\n\x0B\f\r]. 
  // + handles strings with multiple spaces
  myString.split("\\s+")

[xiedaxia1hao]

Primitive Data Type

• In java, Double.MIN_VALUE is actually a positive number, so we have to use -Double.MAX_VALUE or Double.NEGATIVE_INFINITY at the beginning if we want to keep a double value max as the answer.

[xiedaxia1hao]

StringBuilder

StringBuilder sb = new StringBuilder();
sb.append("a"); // append an element to the end
sb.deleteCharAt(sb.length()-1); // delete the last character in the StringBuilder

• StringBuilder的长度是sb.length() 而不是 sb.size() or sb.length！！！