Java中避免空指针检查的方法小结

import java.util.Objects;

public class Foo {
    private Bar bar;

    public Foo(Bar bar) {
        this.bar = Objects.requireNonNull(bar);
    }
}

import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

@NotNull
public static String helloWorld() {
    return "Hello World";
}

@Nullable
public static String helloWorldNullable() {
    return null;
}

public interface Action {
    void doSomething();
}

public interface Parser {
    Action findAction(String userInput);
}

public class MyParser implements Parser {
    private static Action DO_NOTHING = new Action() {
        public void doSomething() { /* do nothing */ }
    };

    public Action findAction(String userInput) {
        // ...
        if ( /* we can't find any actions */ ) {
            return DO_NOTHING;
        }
    }
}

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

public class FruitFinder {
    public static Optional<Fruit> find(String name, List<Fruit> fruits) {
        for (Fruit fruit : fruits) {
            if (fruit.getName().equals(name)) {
                return Optional.of(fruit);
            }
        }
        return Optional.empty();
    }
}

import org.apache.commons.lang3.StringUtils;

public class StringChecker {
    public static void checkString(String foo) {
        if (StringUtils.isBlank(foo)) {
            // do something
        }
    }
}

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

class Fruit {
    private String name;

    public Fruit(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

public class FruitFinder {
    public static Optional<Fruit> find(String name, List<Fruit> fruits) {
        for (Fruit fruit : fruits) {
            if (fruit.getName().equals(name)) {
                return Optional.of(fruit);
            }
        }
        return Optional.empty();
    }

    public static void main(String[] args) {
        List<Fruit> fruits = new ArrayList<>();
        fruits.add(new Fruit("apple"));
        fruits.add(new Fruit("banana"));

        Optional<Fruit> found = find("apple", fruits);
        found.ifPresent(fruit -> System.out.println(fruit.getName()));

        String nameOrFallback = find("lemon", fruits)
               .map(f -> f.getName())
               .orElse("empty-name");
        System.out.println(nameOrFallback);
    }
}

import java.util.Objects;

class Parent {
    private Child child;

    public Parent(Child child) {
        this.child = Objects.requireNonNull(child, "child");
    }
}

class Child {
    // 类的定义
}