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 <T> void sortList(List<T> list, final String sortField, final String sortMode) { if(list == null || list.size() < 2) { return; } Collections.sort(list, new Comparator<T>() { @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<n:i++) { MailSchedule mailSchedule = new MailSchedule(eventstarttime, eventTitle, eventLocation, false); if (!currentDayContentList.contains(mailSchedule)) { currentDayContentList.add(mailSchedule); } } Collections.sort(currentDayContentList);
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<MailSchedule>() { @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