public static <T extends Comparable<? super T>> void sort(List<T> list) { list.sort(null); }
public static <T> void sort(List<T> list, Comparator<? super T> c) { list.sort(c); }
首先使用基本类型(此处使用Integer)来演示第一个方法:
static List<Integer> intList = Arrays.asList(2, 3, 1); //正序 Collections.sort(intList); //倒叙 Collections.sort(intList,new Comparator<Integer>() { @Override public int compare(Integer o1, Integer o2) { // 返回值为int类型,大于0表示正序,小于0表示逆序 return o2-o1; } });
接下来看看自定义类的排序:
public class Emp{ private int empno; private String ename; public int getEmpno() { return empno; } public void setEmpno(int empno) { this.empno = empno; } public String getEname() { return ename; } public void setEname(String ename) { this.ename = ename; } public Emp(int empno, String ename) { super(); this.empno = empno; this.ename = ename; } @Override public String toString() { return "empno:\t"+empno+"\tename:\t"+ename; } }
//定义的list static List<Emp> empList; static { Emp emp1 = new Emp(2,"Guan YunChang"); Emp emp2 = new Emp(3,"Zhang Fei"); Emp emp3 = new Emp(1,"Liu Bei"); empList = Arrays.asList(emp1,emp2,emp3); } //实现排序的方法 Collections.sort(empList,new Comparator<Emp>() { @Override public int compare(Emp o1, Emp o2) { /*按员工编号正序排序*/ return o1.getEmpno()-o2.getEmpno(); /*按员工编号逆序排序*/ //return o2.getEmpno()-o1.getEmpno(); /*按员工姓名正序排序*/ //return o1.getEname().compareTo(o2.getEname()); /*按员工姓名逆序排序*/ //return o2.getEname().compareTo(o1.getEname()); } });
如果直接使用 Collections.sort(empList);需要在Emp类中实现Comparator接口
public class Emp implements Comparable<Emp>{ private int empno; private String ename; public int getEmpno() { return empno; } public void setEmpno(int empno) { this.empno = empno; } public String getEname() { return ename; } public void setEname(String ename) { this.ename = ename; } public Emp(int empno, String ename) { super(); this.empno = empno; this.ename = ename; } @Override public String toString() { return "empno:\t"+empno+"\tename:\t"+ename; } @Override public int compareTo(Emp emp) { /*按员工编号正序排序*/ //return this.getEmpno()-emp.getEmpno(); /*按员工编号逆序排序*/ //return emp.getEmpno()-this.getEmpno(); /*按员工姓名正序排序*/ //return this.getEname().compareTo(emp.getEname()); /*按员工姓名逆序排序*/ return emp.getEname().compareTo(this.getEname()); } }
使用Collections.sort方法的第一种形式实现:
Collections.sort(empList);