java collection.sort() 根据对象的某个属性对list进行排序
１基本类型的list排序
/**
* 对List对象按照某个成员变量进行排序
* @param list List对象
* @param sortField 排序的属性名称
* @param sortMode 排序方式：ASC，DESC 任选其一
*/
public static void sortList(List list, final String sortField, final String sortMode) {
if(list == null || list.size() < 2) {
return;
}
Collections.sort(list, new Comparator() {
@Override
public int compare(T o1, T o2) {
try {
Class clazz = o1.getClass();
Field field = clazz.getDeclaredField(sortField); //获取成员变量
field.setAccessible(true); //设置成可访问状态
String typeName = field.getType().getName().toLowerCase(); //转换成小写
Object v1 = field.get(o1); //获取field的值
Object v2 = field.get(o2); //获取field的值
boolean ASC_order = (sortMode == null || "ASC".equalsIgnoreCase(sortMode));
//判断字段数据类型，并比较大小
if(typeName.endsWith("string")) {
String value1 = v1.toString();
String value2 = v2.toString();
return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1);
}
else if(typeName.endsWith("short")) {
Short value1 = Short.parseShort(v1.toString());
Short value2 = Short.parseShort(v2.toString());
return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1);
}
else if(typeName.endsWith("byte")) {
Byte value1 = Byte.parseByte(v1.toString());
Byte value2 = Byte.parseByte(v2.toString());
return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1);
}
else if(typeName.endsWith("char")) {
Integer value1 = (int)(v1.toString().charAt(0));
Integer value2 = (int)(v2.toString().charAt(0));
return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1);
}
else if(typeName.endsWith("int") || typeName.endsWith("integer")) {
Integer value1 = Integer.parseInt(v1.toString());
Integer value2 = Integer.parseInt(v2.toString());
return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1);
}
else if(typeName.endsWith("long")) {
Long value1 = Long.parseLong(v1.toString());
Long value2 = Long.parseLong(v2.toString());
return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1);
}
else if(typeName.endsWith("float")) {
Float value1 = Float.parseFloat(v1.toString());
Float value2 = Float.parseFloat(v2.toString());
return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1);
}
else if(typeName.endsWith("double")) {
Double value1 = Double.parseDouble(v1.toString());
Double value2 = Double.parseDouble(v2.toString());
return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1);
}
else if(typeName.endsWith("boolean")) {
Boolean value1 = Boolean.parseBoolean(v1.toString());
Boolean value2 = Boolean.parseBoolean(v2.toString());
return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1);
}
else if(typeName.endsWith("date")) {
Date value1 = (Date)(v1);
Date value2 = (Date)(v2);
return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1);
}
else if(typeName.endsWith("timestamp")) {
Timestamp value1 = (Timestamp)(v1);
Timestamp value2 = (Timestamp)(v2);
return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1);
}
else {
//调用对象的compareTo()方法比较大小
Method method = field.getType().getDeclaredMethod("compareTo", new Class[]{field.getType()});
method.setAccessible(true); //设置可访问权限
int result = (Integer)method.invoke(v1, new Object[]{v2});
return ASC_order ? result : result*(-1);
}
}
catch (Exception e) {
String err = e.getLocalizedMessage();
System.out.println(err);
e.printStackTrace();
}
return 0; //未知类型，无法比较大小
}
});
}
2 对自定义对象进行排序
定义对象的代码如下
public class MailSchedule implements Comparable {
private String mTitile;
private Long mLongTime;
private String mTime;
private String mAddress;
private boolean mIsFinish;
public MailSchedule(Long time, String title, String address, boolean isfinish) {
this.mLongTime = time;
this.mTitile = title;
this.mAddress = address;
this.mIsFinish = isfinish;
}
private void getTime(Long time) {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd HH:mm");
String day = sdf.format(new Date(time));
String date = day.split(" ")[0];
String mScheduletime = day.split(" ")[1];
this.mTime = mScheduletime;
}
public Long getLongTime() {
return mLongTime;
}
public String getMailScheduleContent() {
getTime(mLongTime);
return mTime + " " + mTitile + " " + mAddress;
}
public void setIsFinish(boolean isFinish) {
this.mIsFinish = isFinish;
}
public boolean getIsFinish() {
return mIsFinish;
}
public boolean equals(Object obj) {
if (this == obj) {//如果是引用同一个实例
return true;
}
if (obj != null && obj instanceof MailSchedule) {
MailSchedule schedule = (MailSchedule) obj;
return this.mLongTime == schedule.mLongTime && this.mTitile.equals(schedule.mTitile) && this.mAddress.equals(schedule.mAddress);
} else {
return false;
}
}
@Override
public int compareTo(Object comparestu) {
long compareLongTime = ((MailSchedule) comparestu).mLongTime;
return this.mLongTime.compareTo(compareLongTime);
}
}方法一：对象实现 comparable接口，并实现其compareto方法，通过Collections.sort(currentDayContentList)对装有该对象的list排序
for(int i= 0;i方法二：定义一个比较器comparator，通过Collections.sort(currentDayContentList,new comparator())对其list 进行比较
Collections.sort(currentDayContentList, new Comparator() {
@Override
public int compare(MailSchedule lhs, MailSchedule rhs) {
return lhs.getLongTime().compareTo(rhs.getLongTime());
}
}); 3 Arraylist 中contains方法 如下是源码
/**
* Searches this {@code ArrayList} for the specified object.
*
* @param object
* the object to search for.
* @return {@code true} if {@code object} is an element of this
* {@code ArrayList}, {@code false} otherwise
*/
@Override public boolean contains(Object object) {
Object[] a = array;
int s = size;
if (object != null) {
for (int i = 0; i < s; i++) {
if (object.equals(a[i])) {
return true;
}
}
} else {
for (int i = 0; i < s; i++) {
if (a[i] == null) {
return true;
}
}
}
return false;
}从源码中可以发现，会调用调用所比较对象的equals方法，来判断是否为一个对象的实例！现在要对MailSchedule对象进行比较，可以重写equals方法！
如果我们不在MailSchedule类中重写equals()方法的话，虽然我们用contains方法进行了判断，得到的链表的size仍旧是所new对象的个数，因为我们用new关键字创建MailSchedule对象，虽然它们的内容相同，但是JVM虚拟机在堆中开辟了不同存储空间，分别指向不同对象的引用。
需要我们根据MailSchedule的某个属性进行判断，是否为同一个人，我们需要重写equals方法！代码如上面MailSchedule类中的equals方法