\u8fd9\u662f\u4e00\u4e2a\u65b0\u7684\u5de5\u7a0b\u3002\u6211\u4eec\u521b\u5efa\u4e00\u4e2a\u63a5\u53e3\u53eb `PopulationNode`\uff0c\u5b83\u6709\u4e00\u4e2a\u65b9\u6cd5 `computePopulation()`\uff0c\u8868\u793a\u53ef\u4ee5\u8ba1\u7b97\u67d0\u4e2a\u533a\u57df\u7684\u4eba\u53e3\u6570\u91cf\u3002<\/p>\n\n\n\n
\u54ea\u4e9b\u5bf9\u8c61\u53ef\u4ee5\u5177\u6709\u201c\u4eba\u53e3\u201d\u8fd9\u4e2a\u6982\u5ff5\uff1f\u56fd\u5bb6\u3001\u57ce\u5e02\u3001\u533a\u3001\u5c0f\u533a\u3001\u751a\u81f3\u4e00\u680b\u697c\uff0c\u90fd\u53ef\u4ee5\u662f\u4e00\u4e2a\u4eba\u53e3\u8282\u70b9\u3002\u6211\u4eec\u7528\u7ec4\u5408\u6a21\u5f0f\u6765\u7edf\u4e00\u5904\u7406\u8fd9\u79cd\u6811\u5f62\u7ed3\u6784\u3002<\/p>\n\n\n\n
\u6211\u4eec\u5148\u5199\u4e00\u4e2a `City` \u7c7b\uff0c\u5b9e\u73b0 `PopulationNode` \u63a5\u53e3\u3002`City` \u6709\u540d\u5b57\uff0c\u5e76\u4e14\u5305\u542b\u591a\u4e2a\u201c\u533a\u201d\uff08`District`\uff09\u3002\u6bcf\u4e2a `District` \u4e5f\u5b9e\u73b0\u4e86 `PopulationNode`\uff0c\u8868\u793a\u4e00\u4e2a\u884c\u653f\u533a\u57df\uff0c\u5b83\u4e5f\u6709\u540d\u5b57\u548c\u56fa\u5b9a\u7684\u4eba\u53e3\u6570\u3002<\/p>\n\n\n\n
```java
public class District implements PopulationNode {
private final String name;
private final int population;<\/p>\n\n\n\n
public District(String name, int population) {
this.name = name;
this.population = population;
}<\/p>\n\n\n\n
@Override
public int computePopulation() {
return population;
}
}
```<\/p>\n\n\n\n
`City` \u6301\u6709\u4e00\u4e2a `List<District>`\uff0c\u5e76\u63d0\u4f9b `addDistrict(District)` \u65b9\u6cd5\u6765\u6dfb\u52a0\u533a\u3002\u5b83\u7684 `computePopulation()` \u5b9e\u73b0\u4e3a\u6240\u6709\u533a\u7684\u4eba\u53e3\u4e4b\u548c\uff1a<\/p>\n\n\n\n
```java
public class City implements PopulationNode {
private final String name;
private final List<District> districts = new ArrayList<>();<\/p>\n\n\n\n
public void addDistrict(District district) {
districts.add(district);
}<\/p>\n\n\n\n
@Override
public int computePopulation() {
return districts.stream()
.mapToInt(PopulationNode::computePopulation)
.sum();
}
}
```<\/p>\n\n\n\n
\u540c\u7406\uff0c\u6211\u4eec\u518d\u5199\u4e00\u4e2a `Province`\uff08\u7701\uff09\u7c7b\uff0c\u5b83\u4e0d\u76f4\u63a5\u7ba1\u7406\u533a\uff0c\u800c\u662f\u7ba1\u7406\u591a\u4e2a\u57ce\u5e02\uff1a<\/p>\n\n\n\n
```java
public class Province implements PopulationNode {
private final String name;
private final List<City> cities = new ArrayList<>();<\/p>\n\n\n\n
public void addCity(City city) {
cities.add(city);
}<\/p>\n\n\n\n
@Override
public int computePopulation() {
return cities.stream()
.mapToInt(PopulationNode::computePopulation)
.sum();
}
}
```<\/p>\n\n\n\n
\u5728 `main` \u51fd\u6570\u4e2d\uff0c\u6211\u4eec\u53ef\u4ee5\u8fd9\u6837\u7ec4\u88c5\u6570\u636e\uff1a<\/p>\n\n\n\n
```java
Province heilongjiang = new Province(\"\u9ed1\u9f99\u6c5f\");
City harbin = new City(\"\u54c8\u5c14\u6ee8\");
harbin.addDistrict(new District(\"\u5357\u5c97\u533a\", 1000000));
harbin.addDistrict(new District(\"\u9053\u91cc\u533a\", 800000));
heilongjiang.addCity(harbin);<\/p>\n\n\n\n
City jiamusi = new City(\"\u4f73\u6728\u65af\");
jiamusi.addDistrict(new District(\"\u5411\u9633\u533a\", 300000));
heilongjiang.addCity(jiamusi);<\/p>\n\n\n\n
System.out.println(heilongjiang.computePopulation()); \/\/ \u8f93\u51fa\u603b\u4eba\u53e3
```<\/p>\n\n\n\n
\u8fd9\u5c31\u662f\u7ec4\u5408\u6a21\u5f0f\u7684\u5178\u578b\u5e94\u7528\uff1a**\u65e0\u8bba\u662f\u53f6\u5b50\u8282\u70b9\uff08\u5982 `District`\uff09\u8fd8\u662f\u5bb9\u5668\u8282\u70b9\uff08\u5982 `City`\u3001`Province`\uff09\uff0c\u90fd\u5b9e\u73b0\u540c\u4e00\u4e2a\u63a5\u53e3 `PopulationNode`**\u3002\u5ba2\u6237\u7aef\u65e0\u9700\u5173\u5fc3\u5f53\u524d\u64cd\u4f5c\u7684\u662f\u5355\u4e2a\u5bf9\u8c61\u8fd8\u662f\u7ec4\u5408\u5bf9\u8c61\uff0c\u7edf\u4e00\u8c03\u7528 `computePopulation()` \u5373\u53ef\u3002<\/p>\n\n\n\n
\u6211\u4eec\u6253\u4e2a\u65ad\u70b9\u89c2\u5bdf\u6570\u636e\u7ed3\u6784\uff1a`Province` \u5305\u542b\u591a\u4e2a `City`\uff0c\u6bcf\u4e2a `City` \u53c8\u5305\u542b\u591a\u4e2a `District`\u3002\u6574\u4e2a\u7ed3\u6784\u50cf\u4e00\u68f5\u6811\uff0c\u6839\u8282\u70b9\u662f\u7701\uff0c\u4e2d\u95f4\u8282\u70b9\u662f\u57ce\u5e02\uff0c\u53f6\u5b50\u8282\u70b9\u662f\u533a\u3002\u8fd9\u6b63\u662f\u7ec4\u5408\u6a21\u5f0f\u7684\u6838\u5fc3\u601d\u60f3\u2014\u2014\u6811\u5f62\u7ed3\u6784\u7684\u7edf\u4e00\u5904\u7406\u3002<\/p>\n\n\n\n
---<\/p>\n\n\n\n
\u6211\u4eec\u518d\u770b\u53e6\u4e00\u4e2a\u4f8b\u5b50\uff1a\u8ba1\u7b97\u5668\u3002\u6211\u4eec\u60f3\u8ba1\u7b97\u8868\u8fbe\u5f0f `1 + 2 * 3 + 4`\uff0c\u751a\u81f3\u66f4\u590d\u6742\u7684\u5e26\u62ec\u53f7\u7684\u8868\u8fbe\u5f0f\u3002<\/p>\n\n\n\n
\u6211\u4eec\u53ef\u4ee5\u628a\u8868\u8fbe\u5f0f\u770b\u4f5c\u4e00\u68f5\u6811\u3002\u6bd4\u5982 `1 + 2` \u662f\u4e00\u4e2a\u52a0\u6cd5\u8282\u70b9\uff0c\u5de6\u53f3\u5b50\u8282\u70b9\u5206\u522b\u662f\u6570\u5b57 1 \u548c 2\u3002`2 * 3` \u662f\u4e58\u6cd5\u8282\u70b9\uff0c\u4ee5\u6b64\u7c7b\u63a8\u3002<\/p>\n\n\n\n
\u6211\u4eec\u5b9a\u4e49\u4e00\u4e2a\u63a5\u53e3 `Expression`\uff0c\u5b83\u6709\u4e00\u4e2a\u65b9\u6cd5 `getValue()`\uff1a<\/p>\n\n\n\n
```java
public interface Expression {
int getValue();
}
```<\/p>\n\n\n\n
\u53f6\u5b50\u8282\u70b9\u662f `NumberExpression`\uff0c\u8868\u793a\u4e00\u4e2a\u6570\u5b57\uff1a<\/p>\n\n\n\n
```java
public class NumberExpression implements Expression {
private final int value;<\/p>\n\n\n\n
public NumberExpression(int value) {
this.value = value;
}<\/p>\n\n\n\n
@Override
public int getValue() {
return value;
}
}
```<\/p>\n\n\n\n
\u975e\u53f6\u5b50\u8282\u70b9\u662f\u64cd\u4f5c\u7b26\u8868\u8fbe\u5f0f\u3002\u7531\u4e8e\u52a0\u51cf\u4e58\u9664\u90fd\u662f\u4e8c\u5143\u64cd\u4f5c\u7b26\uff0c\u6211\u4eec\u5148\u5199\u4e00\u4e2a\u62bd\u8c61\u57fa\u7c7b `BinaryOperatorExpression`\uff1a<\/p>\n\n\n\n
```java
public abstract class BinaryOperatorExpression implements Expression {
protected final Expression left;
protected final Expression right;<\/p>\n\n\n\n
protected BinaryOperatorExpression(Expression left, Expression right) {
this.left = left;
this.right = right;
}
}
```<\/p>\n\n\n\n
\u7136\u540e\u5177\u4f53\u5b9e\u73b0 `AddExpression`\u3001`SubtractExpression`\u3001`MultiplyExpression`\u3001`DivideExpression`\uff1a<\/p>\n\n\n\n
```java
public class AddExpression extends BinaryOperatorExpression {
public AddExpression(Expression left, Expression right) {
super(left, right);
}<\/p>\n\n\n\n
@Override
public int getValue() {
return left.getValue() + right.getValue();
}
}
```<\/p>\n\n\n\n
\u5176\u4ed6\u64cd\u4f5c\u7b26\u7c7b\u4f3c\u3002<\/p>\n\n\n\n
\u73b0\u5728\u6211\u4eec\u53ef\u4ee5\u624b\u52a8\u6784\u5efa\u8868\u8fbe\u5f0f\u6811\uff1a<\/p>\n\n\n\n
```java
Expression one = new NumberExpression(1);
Expression two = new NumberExpression(2);
Expression three = new NumberExpression(3);
Expression four = new NumberExpression(4);<\/p>\n\n\n\n
Expression add1 = new AddExpression(one, two); \/\/ 1 + 2
Expression mul = new MultiplyExpression(two, three); \/\/ 2 * 3
Expression add2 = new AddExpression(add1, mul); \/\/ (1+2) + (2*3)
Expression total = new AddExpression(add2, four); \/\/ \u4e0a\u8ff0\u7ed3\u679c + 4<\/p>\n\n\n\n
System.out.println(total.getValue());
```<\/p>\n\n\n\n
\u6253\u4e2a\u65ad\u70b9\u53ef\u4ee5\u770b\u5230\uff0c\u6574\u4e2a\u8868\u8fbe\u5f0f\u662f\u4e00\u68f5\u7531 `Expression` \u8282\u70b9\u6784\u6210\u7684\u6811\u3002\u7ec4\u5408\u6a21\u5f0f\u8ba9\u8fd9\u79cd\u7ed3\u6784\u5929\u7136\u6210\u7acb\u3002<\/p>\n\n\n\n
---<\/p>\n\n\n\n
\u4f46\u95ee\u9898\u6765\u4e86\uff1a\u5982\u4f55\u628a\u4e00\u4e2a\u5b57\u7b26\u4e32\u8868\u8fbe\u5f0f\uff08\u5982 `\"1 + 2 * (3 + 4)\"`\uff09\u81ea\u52a8\u89e3\u6790\u6210\u8fd9\u68f5\u6811\uff1f<\/p>\n\n\n\n
\u8fd9\u5c31\u6d89\u53ca\u5230\u8868\u8fbe\u5f0f\u89e3\u6790\u3002\u6211\u4eec\u77e5\u9053\uff1a<\/p>\n\n\n\n
- **\u4e2d\u7f00\u8868\u8fbe\u5f0f**\uff1a\u8fd0\u7b97\u7b26\u5728\u4e2d\u95f4\uff0c\u5982 `1 + 2`\uff0c\u4eba\u7c7b\u6613\u8bfb\uff0c\u8ba1\u7b97\u673a\u96be\u89e3\u6790\u3002
- **\u540e\u7f00\u8868\u8fbe\u5f0f\uff08\u9006\u6ce2\u5170\u5f0f\uff09**\uff1a\u8fd0\u7b97\u7b26\u5728\u540e\u9762\uff0c\u5982 `1 2 +`\uff0c\u8ba1\u7b97\u673a\u6613\u5904\u7406\u3002<\/p>\n\n\n\n
\u8ba1\u7b97\u673a\u901a\u5e38\u5c06\u4e2d\u7f00\u8f6c\u4e3a\u540e\u7f00\uff0c\u518d\u8ba1\u7b97\u3002\u4f8b\u5982\uff1a<\/p>\n\n\n\n
\u4e2d\u7f00\uff1a`(1 + 2) * (3 + 4)`
\u540e\u7f00\uff1a`1 2 + 3 4 + *`<\/p>\n\n\n\n
\u540e\u7f00\u8868\u8fbe\u5f0f\u7684\u8ba1\u7b97\u5f88\u7b80\u5355\uff1a\u7528\u4e00\u4e2a\u6808\uff0c\u4ece\u5de6\u5230\u53f3\u626b\u63cf\uff1a<\/p>\n\n\n\n
- \u9047\u5230\u6570\u5b57\uff0c\u5165\u6808\uff1b
- \u9047\u5230\u64cd\u4f5c\u7b26\uff0c\u5f39\u51fa\u4e24\u4e2a\u6570\u8fdb\u884c\u8fd0\u7b97\uff0c\u7ed3\u679c\u518d\u5165\u6808\uff1b
- \u6700\u540e\u6808\u4e2d\u53ea\u5269\u4e00\u4e2a\u6570\uff0c\u5c31\u662f\u7ed3\u679c\u3002<\/p>\n\n\n\n
\u90a3\u4e48\u5982\u4f55\u5c06\u4e2d\u7f00\u8f6c\u540e\u7f00\uff1f\u89c4\u5219\u5982\u4e0b\uff1a<\/p>\n\n\n\n
1. \u9047\u5230\u64cd\u4f5c\u6570\uff0c\u76f4\u63a5\u52a0\u5165\u8f93\u51fa\uff1b
2. \u9047\u5230 `(`\uff0c\u5165\u6808\uff1b
3. \u9047\u5230 `)`\uff0c\u5c06\u6808\u4e2d\u5143\u7d20\u5f39\u51fa\u5230\u8f93\u51fa\uff0c\u76f4\u5230\u9047\u5230 `(`\uff1b
4. \u9047\u5230\u64cd\u4f5c\u7b26\uff0c\u6bd4\u8f83\u4f18\u5148\u7ea7\uff1a\u82e5\u6808\u9876\u64cd\u4f5c\u7b26\u4f18\u5148\u7ea7 \u2265 \u5f53\u524d\u64cd\u4f5c\u7b26\uff0c\u5219\u5f39\u51fa\u6808\u9876\u5230\u8f93\u51fa\uff0c\u76f4\u5230\u4e0d\u6ee1\u8db3\uff1b\u7136\u540e\u5c06\u5f53\u524d\u64cd\u4f5c\u7b26\u5165\u6808\uff1b
5. \u626b\u63cf\u7ed3\u675f\u540e\uff0c\u5c06\u6808\u4e2d\u5269\u4f59\u64cd\u4f5c\u7b26\u5168\u90e8\u5f39\u51fa\u5230\u8f93\u51fa\u3002<\/p>\n\n\n\n
\u6211\u4eec\u5b9e\u73b0\u4e00\u4e2a `ExpressionParser` \u7c7b\uff1a<\/p>\n\n\n\n
```java
public class ExpressionParser {
private final String infixExpression;<\/p>\n\n\n\n
public ExpressionParser(String expr) {
this.infixExpression = expr.replaceAll(\"\\\\s+\", \"\"); \/\/ \u53bb\u7a7a\u683c
}<\/p>\n\n\n\n
public List<String> toPostfix() {
List<String> output = new ArrayList<>();
Deque<String> stack = new ArrayDeque<>();
int i = 0;<\/p>\n\n\n\n
while (i < infixExpression.length()) {
char c = infixExpression.charAt(i);<\/p>\n\n\n\n
if (Character.isDigit(c)) {
StringBuilder num = new StringBuilder();
while (i < infixExpression.length() && Character.isDigit(infixExpression.charAt(i))) {
num.append(infixExpression.charAt(i++));
}
output.add(num.toString());
i--; \/\/ \u56e0\u4e3a for \u5faa\u73af\u4f1a ++i
} else if (c == '(') {
stack.push(String.valueOf(c));
} else if (c == ')') {
while (!stack.isEmpty() && !stack.peek().equals(\"(\")) {
output.add(stack.pop());
}
stack.pop(); \/\/ \u79fb\u9664 '('
} else if (isOperator(c)) {
while (!stack.isEmpty() && precedence(stack.peek()) >= precedence(String.valueOf(c))) {
output.add(stack.pop());
}
stack.push(String.valueOf(c));
} else {
throw new IllegalArgumentException(\"\u975e\u6cd5\u5b57\u7b26: \" + c);
}
i++;
}<\/p>\n\n\n\n
while (!stack.isEmpty()) {
output.add(stack.pop());
}<\/p>\n\n\n\n
return output;
}<\/p>\n\n\n\n
private boolean isOperator(char c) {
return c == '+' || c == '-' || c == '*' || c == '\/';
}<\/p>\n\n\n\n
private int precedence(String op) {
return switch (op) {
case \"+\", \"-\" -> 1;
case \"*\", \"\/\" -> 2;
default -> 0;
};
}
}
```<\/p>\n\n\n\n
\u63a5\u4e0b\u6765\uff0c\u6211\u4eec\u5c06\u540e\u7f00\u8868\u8fbe\u5f0f\u8f6c\u6362\u4e3a `Expression` \u5bf9\u8c61\u6811\uff1a<\/p>\n\n\n\n
```java
public Expression parse() {
List<String> postfix = toPostfix();
Deque<Expression> stack = new ArrayDeque<>();<\/p>\n\n\n\n
for (String token : postfix) {
if (isOperator(token.charAt(0))) {
Expression right = stack.pop();
Expression left = stack.pop();
Expression expr = switch (token) {
case \"+\" -> new AddExpression(left, right);
case \"-\" -> new SubtractExpression(left, right);
case \"*\" -> new MultiplyExpression(left, right);
case \"\/\" -> new DivideExpression(left, right);
default -> throw new IllegalArgumentException();
};
stack.push(expr);
} else {
int value = Integer.parseInt(token);
stack.push(new NumberExpression(value));
}
}<\/p>\n\n\n\n
return stack.pop();
}
```<\/p>\n\n\n\n
\u4f7f\u7528\u65b9\u5f0f\uff1a<\/p>\n\n\n\n
```java
ExpressionParser parser = new ExpressionParser(\"1 + 2 * (3 + 4)\");
Expression expr = parser.parse();
System.out.println(expr.getValue()); \/\/ \u8f93\u51fa 15
```<\/p>\n\n\n\n
\u6253\u4e2a\u65ad\u70b9\u53ef\u4ee5\u770b\u5230\uff0c\u6700\u7ec8\u751f\u6210\u7684\u662f\u4e00\u68f5\u5b8c\u6574\u7684\u8868\u8fbe\u5f0f\u6811\uff0c\u5b8c\u5168\u7531\u7ec4\u5408\u6a21\u5f0f\u6784\u5efa\u3002<\/p>\n\n\n\n
---<\/p>\n\n\n\n
\u601d\u8003\u9898\uff1a
\u4f60\u80fd\u5b9e\u73b0\u4e00\u4e2a\u652f\u6301\u201c\u4e0a\u4e0b\u6587\u201d\u7684\u8ba1\u7b97\u5668\u5417\uff1f\u6bd4\u5982\u652f\u6301\u53d8\u91cf\u5b9a\u4e49\uff08`x = 5`\uff09\u3001\u51fd\u6570\u8c03\u7528\uff08`sqrt(16)`\uff09\uff0c\u751a\u81f3\u8bb0\u5fc6\u4e0a\u6b21\u8ba1\u7b97\u7ed3\u679c\uff1f\u8fd9\u9700\u8981\u6269\u5c55 `Expression` \u63a5\u53e3\uff0c\u5f15\u5165\u73af\u5883\u4e0a\u4e0b\u6587\uff08`Map<String, Integer>`\uff09\u4f5c\u4e3a `getValue(Context context)` \u7684\u53c2\u6570\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u8fd9\u662f\u4e00\u4e2a\u65b0\u7684\u5de5\u7a0b\u3002\u6211\u4eec\u521b\u5efa\u4e00\u4e2a\u63a5\u53e3\u53eb `PopulationNode`\uff0c\u5b83\u6709\u4e00\u4e2a\u65b9\u6cd5 `computePopulation()`\uff0c …<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"emotion":"","emotion_color":"","title_style":"","license":"","footnotes":""},"categories":[2],"tags":[35],"class_list":["post-1242","post","type-post","status-publish","format-standard","hentry","category-2","tag-35"],"_links":{"self":[{"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/posts\/1242","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/eve2333.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1242"}],"version-history":[{"count":1,"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/posts\/1242\/revisions"}],"predecessor-version":[{"id":1243,"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/posts\/1242\/revisions\/1243"}],"wp:attachment":[{"href":"https:\/\/eve2333.top\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1242"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/eve2333.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1242"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/eve2333.top\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1242"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}