长变量[重复]的Nullpointer异常

Question

我有以下代码

private Long projectNumber; // with getters and setters

当我检查projectnumber是否为null时，我在if条件处得到null指针异常

if(selected.getProjectNumber()!=null){

// do something

}

private Project selected = new Project();

public Project getSelected() {
        return selected;
    }

    public void setSelected(Project selected) {
        this.selected = selected;
    }

public void onRowSelect(SelectEvent event) {

}

public Long getProjectNo() {
            return projectNo;
        }

        public void setProjectNo(Long projectNo) {
            this.projectNo = projectNo;
        }

Answer 1

问题是selected为空。检查如下：

if(selected != null && selected.getProjectNumber()!=null){

   // do something

} else {
   // here: selected = null OR projectNumber of selected is null
}