TestOptional类
import java.util.Optional; import org.junit.Test; /* * 一、Optional 容器类:用于尽量避免空指针异常 * Optional.of(T t) : 创建一个 Optional 实例 * Optional.empty() : 创建一个空的 Optional 实例 * Optional.ofNullable(T t):若 t 不为 null,创建 Optional 实例,否则创建空实例 * isPresent() : 判断是否包含值 * orElse(T t) : 如果调用对象包含值,返回该值,否则返回t * orElseGet(Supplier s) :如果调用对象包含值,返回该值,否则返回 s 获取的值 * map(Function f): 如果有值对其处理,并返回处理后的Optional,否则返回 Optional.empty() * flatMap(Function mapper):与 map 类似,要求返回值必须是Optional */ public class TestOptional { @Test public void test4() { Optional<Employee> op = Optional.of(new Employee(101, "张三", 18, 9999.99)); Optional<String> op2 = op.map(Employee::getName); System.out.println(op2.get()); Optional<String> op3 = op.flatMap((e) -> Optional.of(e.getName())); System.out.println(op3.get()); } @Test public void test3() { Optional<Employee> op = Optional.ofNullable(new Employee()); if (op.isPresent()) { System.out.println(op.get()); } Employee emp = op.orElse(new Employee("张三")); System.out.println(emp); Employee emp2 = op.orElseGet(() -> new Employee()); System.out.println(emp2); } @Test public void test2() { /*Optional<Employee> op = Optional.ofNullable(null); System.out.println(op.get());*/ // Optional<Employee> op = Optional.empty(); // System.out.println(op.get()); } @Test public void test1() { Optional<Employee> op = Optional.of(new Employee()); Employee emp = op.get(); System.out.println(emp); } @Test public void test5() { Man man = new Man(); String name = getGodnessName(man); System.out.println(name); } //需求:获取一个男人心中女神的名字 public String getGodnessName(Man man) { if (man != null) { Godness g = man.getGod(); if (g != null) { return g.getName(); } } return "苍老师"; } //运用 Optional 的实体类 @Test public void test6() { Optional<Godness> godness = Optional.ofNullable(new Godness("林志玲")); Optional<NewMan> op = Optional.ofNullable(new NewMan(godness)); String name = getGodnessName2(op); System.out.println(name); } public String getGodnessName2(Optional<NewMan> man) { return man.orElse(new NewMan()) .getGodness() .orElse(new Godness("苍老师")) .getName(); } }
Man类
@Data public class Man { private Godness god; public Man() {}
public Man(Godness god) { this.god = god; } }
Godness类
@Data public class Godness { private String name; public Godness() {} public Godness(String name) { this.name = name; } }
NewMan类
import java.util.Optional; //注意:Optional 不能被序列化 public class NewMan { private Optional<Godness> godness = Optional.empty(); private Godness god; public Optional<Godness> getGod(){ return Optional.of(god); } public NewMan() {} public NewMan(Optional<Godness> godness) { this.godness = godness; } }