如何在 Java 中替换多个 if 语句
如何在 Java 中替换多个 if 语句
1. 工厂类
定义一个具有单个apply方法的Operation接口：
public interface Operation {
int apply(int a, int b);
}
该方法将两个数字作为输入并返回结果。让我们定义两个执行加法的类：
public class Addition implements Operation {
@Override
public int apply(int a, int b) {
return a + b;
}
}
public class Reduce implements Operation {
@Override
public int apply(int a, int b) {
return a - b;
}
}
我们现在将实现一个工厂类，它根据给定的运算符返回Operation的实例：
import java.util.HashMap;
import java.util.Map;
import java.util.Optional;
public class OperatorFactory {
static Map<String, Operation> operationMap = new HashMap<>();
static {
operationMap.put("add", new Addition());
operationMap.put("reduce", new Reduce());
// more operators
}
public static Optional<Operation> getOperation(String operator) {
return Optional.ofNullable(operationMap.get(operator));
}
}
现在，在Calculator类中，我们可以查询工厂以获取相关操作并应用于：
public class Calculator {
@Test
public void use(){
System.out.println(calculateUsingFactory(1,2,"add"));
}
public int calculateUsingFactory(int a, int b, String operator) {
Operation targetOperation = OperatorFactory
.getOperation(operator)
.orElseThrow(() -> new IllegalArgumentException("Invalid Operator"));
return targetOperation.apply(a, b);
}
}
2. 枚举的使用
除了使用Map，我们还可以使用Enum来标注特定的业务逻辑
我们将为每个Enum值定义方法并进行计算 需要导入google的 guava工具类
import com.google.common.collect.Maps;
import lombok.AllArgsConstructor;
import lombok.Getter;
import javax.annotation.Nullable;
import java.util.Arrays;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.Map;
@Getter
@AllArgsConstructor
public enum OperatorEnum {
ADD(1) {
@Override
public int apply(int a, int b) {
return a + b;
}
},
MULTIPLY(2) {
@Override
public int apply(int a, int b) {
return a * b;
}
},
SUBTRACT(3) {
@Override
public int apply(int a, int b) {
return a - b;
}
},
DIVIDE(4) {
@Override
public int apply(int a, int b) {
return a / b;
}
},
MODULO(5) {
@Override
public int apply(int a, int b) {
return a % b;
}
};
public abstract int apply(int a, int b);
private final Integer operator;
private static final Map<Integer, OperatorEnum> LOOKUP = Maps.uniqueIndex(
Arrays.asList(OperatorEnum.values()),
OperatorEnum::getOperator
);
@Nullable
public static OperatorEnum reversion(int status) {
return LOOKUP.get(status);
}
}
也可以使用实现
public interface Operator {
int apply(int a, int b);
}
import com.google.common.collect.Maps;
import lombok.AllArgsConstructor;
import lombok.Getter;
import javax.annotation.Nullable;
import java.util.Arrays;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.Map;
@Getter
@AllArgsConstructor
public enum OperatorEnum implements Operator{
ADD(1) {
@Override
public int apply(int a, int b) {
return a + b;
}
},
MULTIPLY(2) {
@Override
public int apply(int a, int b) {
return a * b;
}
},
SUBTRACT(3) {
@Override
public int apply(int a, int b) {
return a - b;
}
},
DIVIDE(4) {
@Override
public int apply(int a, int b) {
return a / b;
}
},
MODULO(5) {
@Override
public int apply(int a, int b) {
return a % b;
}
};
private final Integer operator;
private static final Map<Integer, OperatorEnum> LOOKUP = Maps.uniqueIndex(
Arrays.asList(OperatorEnum.values()),
OperatorEnum::getOperator
);
@Nullable
public static OperatorEnum reversion(int status) {
return LOOKUP.get(status);
}
}
测试方法
public class Calculator {
public int calculate(int a, int b, OperatorEnum operator) {
return operator.apply(a, b);
}
@Test
public void use(){
System.out.println(calculate(1,2,OperatorEnum.reversion(1)));
}
}
3. 命令模式
我们将首先定义我们的Command接口：
public interface Command {
Integer execute();
}
接下来，让我们实现一个AddCommand：
public class AddCommand implements Command {
private final int a;
private final int b;
public AddCommand(int a, int b) {
this.a = a;
this.b = b;
}
@Override
public Integer execute() {
return a + b;
}
}
最后，让我们在Calculator中引入一个接受并执行Command的新方法：
public class Calculator {
public int calculate(Command command) {
return command.execute();
}
@Test
public void whenCalculateUsingCommand_thenReturnCorrectResult() {
Calculator calculator = new Calculator();
int result = calculator.calculate(new AddCommand(3, 7));
assertEquals(10, result);
}
}
4. Map+函数式接口
定义一个方法类
public class Operator {
public static int add(int a,int b){
return a+b;
}
public static int multiply(int a,int b){
return a*b;
}
public static int subtract(int a,int b){
return a-b;
}
}
配置
配置一个实现工厂
import java.util.HashMap;
import java.util.Map;
import java.util.function.BiFunction;
public class QueryGrantTypeService {
// 两个参数使用 BiFunction 单个参数使用 Function 不需要返回值使用 Consumer消费函数 多个参数使用Function3 Function4
private static Map<String, BiFunction<Integer,Integer,Integer>> grantTypeMap=new HashMap<>();
// 静态代码块可以替换@PostConstruct
static{
grantTypeMap.put("add",(a,b)->Operator.add(a,b));
grantTypeMap.put("subtract",(a,b)->Operator.subtract(a,b));
grantTypeMap.put("multiply",(a,b)->Operator.multiply(a,b));
}
public Integer getResult(String resourceType,int a ,int b){
BiFunction<Integer,Integer,Integer> result=grantTypeMap.get(resourceType);
return result.apply(a,b);
}
}
具体调用
public class Calculator {
@Test
public void use(){
System.out.println(new QueryGrantTypeService().getResult("add",1,2));
}
}
5. Vavr模式匹配
@Test
public void whenMatchworks_thenCorrect() {
String arg="--help";
Match(arg).of(
Case($ (isIn("-h", "--help")), o -> run(this::displayHelp)),
Case($(isIn("-v", "--version")), o -> run(this::displayVersion)),
Case($(), o -> run(() -> {
throw new IllegalArgumentException(arg);
}))
);
}
private void displayVersion(){
System.out.println("--version");
}
private void displayHelp(){
System.out.println("--help");
}