Stream中过滤null的情形
class Customer {
private Long id;
private String name;
public Customer(Long id, String name) {
this.id = id;
this.name = name;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
List<Customer> customerList = new ArrayList<>();
customerList.add(new Customer(1L, "Ryu"));
customerList.add(new Customer(2L, "Ken"));
customerList.add(new Customer(3L, null));
customerList.add(new Customer(5L, null));
customerList.add(new Customer(null, "Zangief"));
要求查询出id不是5的列表数据:
普通写法:
List<Customer> customers = customerList.stream().filter(x ->5L!=x.getId()).collect(Collectors.toList());
这个语句会抛出异常,因为列表中有一条数据id为null
但是如果过滤的是Name,String类型的就没有问题。
测验数字与null对比:
int a=1;
Integer aa=null;
Integer bb=1;
//System.out.println(aa.equals(a)); //aa为null,error
//System.out.println(aa == a); //aa为null,error
//System.out.println(a == aa);//aa为null,error
System.out.println(bb.equals(aa));
System.out.println(bb == aa);
System.out.println(aa==bb);
当aa=1,这个时候没有任何问题
但是当aa=null,上面3种方式都会抛出异常, java.lang.NullPointerException
结果
经过这样的判断,上述的filter
代码可以优化为:
List<Customer> customers = customerList.stream().filter(x ->!Long.valueOf(5L).equals(x.getId())).collect(Collectors.toList());
所以遇到基本数据类型,最好还是转换成类型处理