数组工具类

 

    @Test

    public void test1() {

        String[] str = new String[] { "Jack", "Alex", "Ami", "Jerry" };

        Arrays.sort(str);

        // 显示已经排序的数据

        System.err.println(Arrays.toString(str));

    }

 

 

    @Test

    public void test1() {

        String[] str = new String[] { "Jack", "Alex", "Ami", "Jerry" };

        Arrays.sort(str, 1, 3);

        // 显示已经排序的数据

        System.err.println(Arrays.toString(str));

    }

  

在sort里面，若是想实现对对象排序，你的类必需要实现：

 

 两种:

   1:实现接口comparable

   2:提供一个比较器。

 

public class Demo03 {

    @Test

    public void test1() {

        // 默认全部系统的类Int,Integer,double ,float ,String能够排序

        Stud[] studs = new Stud[] { new Stud("Jerry"), new Stud("Alex"), new Stud("Jack") };

        Arrays.sort(studs);

        System.err.println(Arrays.toString(studs));

    }

 

    class Stud implements Comparable<Stud> {

        private String name;

 

        public Stud(String name) {

            this.name = name;

        }

 

        @Override

        public String toString() {

            return "Stud [name=" + name + "]";

        }

 

        @Override

        public int compareTo(Stud o) {

            return o.name.compareTo(this.name);

        }

    }

}

 

package cn.demo;

 

import java.lang.reflect.Array;

import java.util.Arrays;

import java.util.Comparator;

 

import org.junit.Test;

 

public class Demo03 {

    @Test

    public void test1() {

        // 默认全部系统的类Int,Integer,double ,float ,String能够排序

        Stud[] studs = new Stud[] { new Stud("Jerry"), new Stud("Alex"), new Stud("Jack") };

        Arrays.sort(studs, new Comparator<Stud>() {

            @Override

            public int compare(Stud o1, Stud o2) {

                return o2.getName().compareTo(o1.getName());

            }

        });

        System.err.println(Arrays.toString(studs));

    }

 

}

 

class Stud {

    private String name;

 

    public Stud(String name) {

        this.name = name;

    }

 

    public String getName() {

        return name;

    }

    @Override

    public String toString() {

        return "Stud [name=" + name + "]";

    }

}

class Stud {

    private String name;

    private int age;

 

    public Stud(String name, int age) {

        this.name = name;

        this.age = age;

    }

 

    public String getName() {

        return name;

    }

 

    @Override

    public String toString() {

        return "Stud [name=" + name + ", age=" + age + "]";

    }

 

}

 

 

public class Demo04 {

    @Test

    public void test1(){

       int[] a = {22,33,445};

       Arrays.fill(a, 100);//所有设置成100

       System.err.println(Arrays.toString(a));

    }

}

 

[100, 100, 100]

 

 

    @Test

    public void test1() {

       int[] a1 = { 22, 33, 445 };// new Int[]{}...

       int[] a2 = { 22, 33, 445 };// new int[]{}

       System.err.println(a1 == a2);// false

       System.err.println(a1.equals(a2));// false;   内存地址不相等

       boolean boo = Arrays.equals(a1, a2);

       System.err.println(boo);// true

    }

 

 

    @Test

    public void test1() {

       int[] a1 = { 22, 33, 445 };// new Int[]{}...

       int[] a2 = Arrays.copyOf(a1, 5);//数组增加

       System.err.println(Arrays.toString(a2));

    }

 

public class Demo04 {

    @Test

    public void test1() {

       int[] a1 = { 22, 33, 445 };// new Int[]{}...

       int[] a2 = Arrays.copyOfRange(a1, 1, 3);// >=from and <to

       System.err.println(Arrays.toString(a2));

    }

}

 

关于二分法查找 本身能够开发出来:

 原则：只能查询已经排过序的数组。

 

public class Demo04 {

    @Test

    public void test1() {

       int[] a = { 1, 2, 3, 4, 5, 6 };

       int num = -5;

       int left = 0;

       int right = a.length - 1;

       int idx = -1;

       while (left <= right) {

           int mid = (left + right) / 2;

           int no = a[mid];

           if (num > no) {

              left = mid + 1;

           } else if (num < no) {

              right = mid - 1;

           } else {

              idx = mid;

              break;

           }

       }

       System.err.println("index is:" + idx);

    }

}

 

 

@Test

    public void test2() {

       int[] a = {5,6,7,78,54,3,3,3 , 2, 4, 6, 8 };

       Arrays.sort(a);

       int idx = Arrays.binarySearch(a, 7);

       System.err.println(idx);

    }