java常用开发工具类

 Arrays类

import java.util.Arrays;

//int[] array = new int[]{2,1,5,4}; Arrays.asList()不能应用于基本数据类型
Integer[] array = new Integer[]{2,1,5,4};
Integer[] array1 = new Integer[]{2,2,3,4};

List<Integer> list = Arrays.asList(array);
Arrays.sort(array);
int index = Arrays.binarySearch(array,4);
System.out.println(Arrays.toString(array));
boolean isEqual = Arrays.equals(array,array2);
Arrays.sort(array);//还可以按照自定义去排序

Collections类 

import java.util.Collections;
//处理set map list
import java.util.List;
import java.util.ArrayList;

List<Integer> list = new ArrayList<>();
list.add(4);
list.add(5);
list.add(6);

//最大值，最小值
int max = Collections.max(list);
int min = Collections.min(list);

Collections.reverse(list);//反转

int frequency = Collections.frequency(list,4);//频率

Collections.shuffle(list);//重新洗牌

Collections.sort(list);//升序

List<Student> students = new ArrayList<>();
students.add(new Student(3, "李四"));
students.add(new Student(1, "张三"));
students.add(new Student(2, "王五"));
// 按照id排序
Collections.sort(students, (s1, s2) -> Integer.compare(s1.getId(), s2.getId()));

Objects类 

import java.util.Objects;

//equals()
String s1 = null;
String s2 = "abc";
boolean equals = Objects.equals(s1,s2);

Optional类