代码
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import java.util.Optional;
public class OptionalDemo3 {
static class Category {
private String name;
public Category(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Category{" +
"name='" + name + '\'' +
'}';
}
}
static class Goods {
private String name;
private Category category;
public Goods() {
}
public Goods(String name, Category category) {
this.name = name;
this.category = category;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Category getCategory() {
return category;
}
public void setCategory(Category category) {
this.category = category;
}
@Override
public String toString() {
return "Good{" +
"name='" + name + '\'' +
", category=" + category +
'}';
}
}
/**
* 获取商品的分类名称（使用 Optional 类包装）
* @param goods 商品
* @return 分类名称
*/
static String getGoodsCategoryName(Goods goods) {
// 将商品实例包装入 Optional 类，创建 Optional<Goods> 对象
Optional<Goods> goodsOptional = Optional.ofNullable(goods);
Goods goods1 = goodsOptional.orElse(new Goods("默认商品", new Category("默认分类")));
// 此时 goods1 一定是非空，不会产生空指针异常
Category category = goods1.getCategory();
// 将分类实例包装入 Optional 类，创建 Optional<Category> 对象
Optional<Category> categoryOptional = Optional.ofNullable(category);
Category category1 = categoryOptional.orElse(new Category("默认分类"));
// 此时 category1 一定是非空，不会产生空指针异常
return category1.getName();
}
public static void main(String[] args) {
// 实例化一个商品类
Goods goods = null;
// 获取商品的分类名称
String categoryName = getGoodsCategoryName(goods);
System.out.println(categoryName);
}
}
运行结果