交换数据

首先我们要学会如何对调

package com.itheima.loopdemo;
import java.util.Random;
public class test {
    public static void main(String[] args){
        int a = 10;
        int b = 20;
        int temp = a;
        a = b;
        b = temp;
        System.out.println(a);
        System.out.println(b);
    }
}

之后学习数组中的调换

package com.itheima.loopdemo;
import java.util.Random;

public class test {
    public static void main(String[] args){
        int[] array = {1,2,3,4,5};
        int temp = array[0];
        array[0] = array[4];
        array[4] = temp;
        for (int i = 0; i < array.length; i++) {
            System.out.print(array[i]);
        }
    }
}

如果数据比较大并且要从头到尾转换,我们可以这样做

package com.itheima.loopdemo;
import java.util.Random;

public class test {
    public static void main(String[] args){
        int[] array = {1,2,3,4,5};
        for (int i = 0,j = array.length - 1; i < j; i++,j--) {
            int temp = array[i];
            array[i] = array[j];
            array[j] = temp;
        }
        for (int i = 0; i < array.length; i++) {
            System.out.print(array[i] +"");
        }
    }
}

打乱数据

package com.itheima.loopdemo;

import java.util.Random;

public class test {
    public static void main(String[] args) {
        int[] array = {1, 2, 3, 4, 5};
        Random r = new Random();
        for (int i = 0; i < array.length; i++) {
            int RandomIndex = r.nextInt(array.length);
            int temp = array[i];
            array[i] = array[RandomIndex];
            array[RandomIndex] = temp;
        }
        for (int i = 0; i < array.length; i++) {
            System.out.print(array[i]+ " ");
        }
    }
}

数组内存图

Java内存分配

方法

什么是方法?

方法的格式

最简单方法定义和调用方式

package com.itheima.loopdemo;

import java.util.Random;

public class test {
    public static void main(String[] args) {
        //调用方法
        study();
        study();
    }
    //定义一个方法
    public static void study(){
        System.out.println("学习!");
    }
}

带参数的方法定义和调用

package com.itheima.loopdemo;

import java.util.Random;

public class test {
    public static void main(String[] args) {
        study(10, 20);
    }

    //定义一个方法
    public static void study(int num1, int num2) {
        int result = num1 + num2;
        System.out.println(result);
    }
}

带返回值方法的定义和调用

package com.itheima.loopdemo;

public class test {
    public static void main(String[] args) {
        double Area1 = GetArea(2.8, 1.9);
        double Area2 = GetArea(2.5, 2.1);
        if (Area1 > Area2) {
            System.out.println("第一个长方形的面积更大");
        } else {
            System.out.println("第二个长方形的面积更大");
        }
    }
    public static double GetArea(double len, double width) {
        double Area = len * width;
        return Area;
    }
}

方法的完整定义格式

方法的重载

package com.itheima.loopdemo;

public class test {
    public static void main(String[] args) {
        int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9};
        int[] copy = CopyOfRange(array,3,7);
        for (int i = 0; i < copy.length; i++) {
            System.out.print(copy[i]);
            }
    }
    public static int[] CopyOfRange(int[] array, int from, int to) {
        int[] NewArray = new int[to - from];
        int index = 0;
        for (int i = from; i < to; i++) {
             NewArray[index] = array[i];
             index++;
        }return NewArray;
    }
}

目前学习进度: