Java 消除 if else 代码的几种方式

提前 return

优化前

if(condition) { 
    //doSomething 
} else { 
    return; 
} 

优化后

if（!condition）{ 
    return; 
} 
//doSomething 

使用三元运算符

优化前

int price; 
if(condition) { 
    price = 80; 
} else { 
    price = 100; 
} 

优化后

int price = condition ? 80 : 100;

使用枚举

优化前

int status = 0;
String orderStatus;
if (status == 0) {
    orderStatus = "UNPAID";
} else if (status == 1) {
    orderStatus = "PAID";
} else {
    orderStatus = "PAYING";
}

优化后

public class EnumDemo {

    public static void main(String[] args) {
        int status = 0;
        String orderStatus = OrderStatus.of(status);
    }

    private enum OrderStatus {
        UNPAID(0,"未支付"),
        PAID(1,"已支付"),
        PAYING(2, "支付中");

        private int code;
        private String label;

        OrderStatus(int code, String label) {
            this.code = code;
            this.label = label;
        }

        public static String of(int code) {
            for(OrderStatus s : OrderStatus.values()) {
                if(s.code == code) {
                    return s.label;
                }
            }
            return "";
        }
    }
}

使用 Optional

优化前

String s = "hello world";

if (s != null) {
    System.out.println(s);
} else {
    System.out.println("str is empty");
}

优化后：Java9之后Optional增加的ifPresentOrElse()方法

String s = "hello world";
Optional.of(s).ifPresentOrElse(System.out::println, () -> System.out.println("empty str"));

表驱动法

优化前

String param = "one";
if ("one".equals(param)) {
    System.out.println(param.toUpperCase());
} else if ("two".equals(param)) {
    System.out.println(param.toLowerCase());
} else if ("three".equals(param)) {
    System.out.println(param.trim());
}

优化后

String param = "one";
HashMap<String, Function<String, String>> map = new HashMap<>();

map.put("one", String::toUpperCase);
map.put("two", String::toLowerCase);
map.put("three", String::trim);

String apply = map.get("three").apply("abc");
System.out.println(apply);

策略模式+工厂方法

优化前

String param = "one";
if ("one".equals(param)) {
    System.out.println("this is one");
} else if ("two".equals(param)) {
    System.out.println("this is two");
} else if ("three".equals(param)) {
    System.out.println("this is three");
}

优化后

public class StrategyAndFactoryDemo {

    public static void main(String[] args) {
        IStrategy strategy = StrategyFactory.getStrategy("two");
        strategy.doSomething();
    }

    private static class StrategyFactory {
        private static final Map<String, IStrategy> map = new HashMap<>();
        static {
            map.put("one", new StrategyOne());
            map.put("two", new StrategyTwo());
            map.put("three", new StrategyThree());
        }

        public static IStrategy getStrategy(String index) {
            return map.get(index);
        }
    }

    private interface IStrategy {
        void doSomething();
    }

    private static class StrategyOne implements IStrategy {

        @Override
        public void doSomething() {
            System.out.println("this is strategy one");
        }
    }

    private static class StrategyTwo implements IStrategy {

        @Override
        public void doSomething() {
            System.out.println("this is strategy two");
        }
    }

    private static class StrategyThree implements IStrategy {

        @Override
        public void doSomething() {
            System.out.println("this is strategy three");
        }
    }

}