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java 判斷對象是否為空
java 中如何判斷對象是否為空呢,特別是一個未知的對象?
下麵是一個通用的方法，判斷字符串是否為空，集合是否為空，數組是否為空：
/**
* 判斷對象或對象數組中每一個對象是否為空: 對象為null，字符序列長度為0，集合類、Map為empty
*
* @param obj
* @return
*/
public static boolean isNullOrEmpty(Object obj) {
if (obj == null)
return true;
if (obj instanceof CharSequence)
return ((CharSequence) obj).length() == 0;
if (obj instanceof Collection)
return ((Collection) obj).isEmpty();
if (obj instanceof Map)
return ((Map) obj).isEmpty();
if (obj instanceof Object[]) {
Object[] object = (Object[]) obj;
if (object.length == 0) {
return true;
}
boolean empty = true;
for (int i = 0; i < object.length; i++) {
if (!isNullOrEmpty(object[i])) {
empty = false;
break;
}
}
return empty;
}
return false;
}
上述方法運用了遞歸,當對象是數組時又調用自身.
測試:
@Test
public void test_isNullOrEmpty(){
String input1=null;
String input3="";
String input4=" ";
String input5="a";
String input6=" ";
String[] strs1 = new String[] { "a" };
String[] strs2 = new String[] { "", "" };
String[] strs3 = new String[] { "", "c" };
String[] strs4 = new String[] {};
org.junit.Assert.assertEquals(true, ValueWidget.isNullOrEmpty(input1));
org.junit.Assert.assertEquals(true, ValueWidget.isNullOrEmpty(input3));
org.junit.Assert.assertEquals(false, ValueWidget.isNullOrEmpty(input4));
org.junit.Assert.assertEquals(false, ValueWidget.isNullOrEmpty(input5));
org.junit.Assert.assertEquals(false, ValueWidget.isNullOrEmpty(input6));
org.junit.Assert.assertEquals(false, ValueWidget.isNullOrEmpty(strs1));
org.junit.Assert.assertEquals(true, ValueWidget.isNullOrEmpty(strs2));
org.junit.Assert.assertEquals(false, ValueWidget.isNullOrEmpty(strs3));
org.junit.Assert.assertEquals(true, ValueWidget.isNullOrEmpty(strs4));
}
那麼如何判斷一個自定義對象屬性是否全為空呢?(這裏隻考慮對象的屬性全為基本類型)?
代碼如下:
/***
* Determine whether the object's fields are empty
*
* @param obj
* @param isExcludeZero :true:數值類型的值為0,則當做為空;----false:數值類型的值為0,則不為空
*
* @return
* @throws SecurityException
* @throws IllegalArgumentException
* @throws NoSuchFieldException
* @throws IllegalAccessException
*/
public static boolean isNullObject(Object obj, boolean isExcludeZero)
throws SecurityException, IllegalArgumentException,
NoSuchFieldException, IllegalAccessException {
List<Field> fieldList = ReflectHWUtils.getAllFieldList(obj.getClass());
boolean isNull = true;
for (int i = 0; i < fieldList.size(); i++) {
Field f = fieldList.get(i);
Object propertyValue = null;
try {
propertyValue = getObjectValue(obj, f);
} catch (NoSuchFieldException e) {
e.printStackTrace();
}
if (!ValueWidget.isNullOrEmpty(propertyValue)) {// 字段不為空
if (propertyValue instanceof Integer) {// 是數字
if (!((Integer) propertyValue == 0 && isExcludeZero)) {
isNull = false;
break;
}
} else if (propertyValue instanceof Double) {// 是數字
if (!((Double) propertyValue == 0 && isExcludeZero)) {
isNull = false;
break;
}
}else if (propertyValue instanceof Float) {// 是數字
if (!((Float) propertyValue == 0 && isExcludeZero)) {
isNull = false;
break;
}
}else if (propertyValue instanceof Short) {// 是數字
if (!((Short) propertyValue == 0 && isExcludeZero)) {
isNull = false;
break;
}
}else {
isNull = false;
break;
}
}
}
return isNull;
}
ValueWidget.isNullOrEmpty 的類com.string.widget.util.ValueWidget.ValueWidget:見
https://download.csdn.net/detail/hw1287789687/7255307
測試:
package com.test.bean;
import java.sql.Timestamp;
public class Person2 {
private int id;
private int age;
private double weight;
private String personName;
private Timestamp birthdate;
public String identitify;
protected String address;
String phone;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getPersonName() {
return personName;
}
public void setPersonName(String personName) {
this.personName = personName;
}
public Timestamp getBirthdate() {
return birthdate;
}
public void setBirthdate(Timestamp birthdate) {
this.birthdate = birthdate;
}
public String getIdentitify() {
return identitify;
}
public void setIdentitify(String identitify) {
this.identitify = identitify;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
public double getWeight() {
return weight;
}
public void setWeight(double weight) {
this.weight = weight;
}
}
@Test
public void test_isNullObject() throws SecurityException,
IllegalArgumentException, NoSuchFieldException,
IllegalAccessException {
Person2 p = new Person2();
Assert.assertEquals(true, ReflectHWUtils.isNullObject(p, true));
Assert.assertEquals(false, ReflectHWUtils.isNullObject(p, false));
p.setAddress("beijing");
Assert.assertEquals(false, ReflectHWUtils.isNullObject(p, true));
Assert.assertEquals(false, ReflectHWUtils.isNullObject(p, false));
p.setAddress(null);
p.setId(0);
Assert.assertEquals(true, ReflectHWUtils.isNullObject(p, true));
Assert.assertEquals(false, ReflectHWUtils.isNullObject(p, false));
}參考:https://hw1287789687.iteye.com/blog/1936364項目代碼下載地址:
https://download.csdn.net/detail/hw1287789687/7255307
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最後更新：2017-04-03 12:56:25