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day05

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标签:oat   讲解   比较   常见操作   byte   har   执行   声明   查找   

1:方法(掌握)

         (1)方法:就是完成特定功能的代码块。

                   注意:在很多语言里面有函数的定义,而在Java中,函数被称为方法。

         (2)格式:

                   修饰符 返回值类型 方法名(参数类型 参数名1,参数类型 参数名2...) {

                            方法体语句;

                            return 返回值;

                   }

 

                   修饰符:目前就用 public static。后面再详细讲解其他修饰符

                  返回值类型:就是功能结果的数据类型

                   方法名:就是起了一个名字,方便我们调用该方法。

                   参数类型:就是参数的数据类型

                   参数名:就是变量

                   参数分类:

                            实参:实际参与运算的数据

                            形参:方法上定义的,用于接收实际参数的变量

                   方法体语句:就是完成功能的代码块

                   return:结束方法

                   返回值:就是功能的结果,由return带给调用者。

         (3)两个明确:

                   返回值类型:结果的数据类型

                   参数列表:参数的个数及对应的数据类型

         (4)方法调用

                   A:有明确返回值的方法

                            a:单独调用,没有意义

                            b:输出调用,不是很好,因为我可能需要不结果进行进一步的操作。但是讲课一般我就用了。

                            c:赋值调用,推荐方案

                   B:void类型修饰的方法

                            a:单独调用

         (5)案例:

                   A:求和方案

                   B:获取两个数中的较大值

                   C:比较两个数据是否相同

                   D:获取三个数中的最大值

                   E:输出m行n列的星形

                   F:输出nn乘法表

         (6)方法的注意事项

                   A:方法不调用不执行

                   B:方法之间是平级关系,不能嵌套定义

                   C:方法定义的时候,参数是用,隔开的

                   D:方法在调用的时候,不用在传递数据类型

                   E:如果方法有明确的返回值类型,就必须有return语句返回。

         (7)方法重载

                   在同一个类中,方法名相同,参数列表不同。与返回值无关。

                  

                   参数列表不同:

                            参数的个数不同。

                            参数的对应的数据类型不同。

         (8)方法重载案例

                   不同的类型的多个同名方法的比较。

                  

2:数组(掌握)

         (1)数组:存储同一种数据类型的多个元素的容器。

         (2)特点:每一个元素都有编号,从0开始,最大编号是长度-1。

                  编号的专业叫法:索引

         (3)定义格式

                   A:数据类型[] 数组名;

                   B:数据类型 数组名[];

                  

                   推荐是用A方式,B方法就忘了吧。

                   但是要能看懂

         (4)数组的初始化

                   A:动态初始化

                            只给长度,系统给出默认值

                           

                            举例:int[] arr = new int[3];

                   B:静态初始化

                            给出值,系统决定长度

                           

                            举例:int[] arr = new int[]{1,2,3};

                            简化版:int[] arr = {1,2,3};

         (5)Java的内存分配[陈文文1] 

                   A:栈 存储局部变量

                   B:堆 存储所有new出来的

                   C:方法区(面向对象部分详细讲解)

                   D:本地方法区(系统相关)

                   E:寄存器(CPU使用)

                  

                   注意:

                            a:局部变量 在方法定义中或者方法声明上定义的变量。

                            b:栈内存和堆内存的区别

                                     栈:数据使用完毕,就消失。

                                     堆:每一个new出来的东西都有地址

                                         每一个变量都有默认值

                                                        byte,short,int,long 0

                                                        float,double 0.0

                                                        char ‘\u0000‘

                                                        boolean false

                                                        引用类型 null

                                         数据使用完毕后,在垃圾回收器空闲的时候回收。

         (6)数组内存图

                   A:一个数组

                   B:二个数组

                   C:三个数组(两个栈变量指向同一个堆内存)

         (7)数组的常见操作

                   A:遍历

                            方式1:

                                     public static void printArray(int[] arr) {

                                               for(int x=0; x<arr.length; x++) {

                                                        System.out.println(arr[x]);

                                               }

                                     }

                                    

                            方式2:

                                     public static void printArray(int[] arr) {

                                               System.out.print("[");

                                               for(int x=0; x<arr.length; x++) {

                                                        if(x == arr.length-1) {

                                                                 System.out.println(arr[x]+"]");

                                                        }else {

                                                                  System.out.println(arr[x]+", ");

                                                        }

                                               }

                                     }

                   B:最值

                            最大值:

                                     public static int getMax(int[] arr) {

                                               int max = arr[0];

                                              

                                               for(int x=1; x<arr.length; x++) {

                                                        if(arr[x] > max) {

                                                                 max = arr[x];

                                                        }

                                               }

                                              

                                               return max;

                                     }

                                    

                            最小值:

                                     public static int getMin(int[] arr) {

                                               int min = arr[0];

                                              

                                               for(int x=1; x<arr.length; x++) {

                                                        if(arr[x] < min) {

                                                                 min = arr[x];

                                                        }

                                               }

                                              

                                               return min;

                                     }

                   C:逆序

                            方式1:

                                     public static void reverse(int[] arr) {

                                               for(int x=0; x<arr.length/2; x++) {

                                                        int temp = arr[x];

                                                        arr[x] = arr[arr.length-1-x];

                                                        arr[arr.length-1-x] = temp;

                                               }

                                     }

                                    

                            方式2:

                                     public static void reverse(int[] arr) {

                                               for(int start=0,end=arr.length-1; start<=end; start++,end--) {

                                                        int temp = arr[start];

                                                        arr[start] = arr[end];

                                                        arr[end] = temp;

                                               }

                                     }

                   D:查表

                                     public static String getString(String[] strArray,int index) {

                                               return strArray[index];

                                     }

                   E:基本查找

                            方式1:

                                     public static int getIndex(int[] arr,int value) {

                                               for(int x=0; x<arr.length; x++) {

                                                        if(arr[x] == value) {

                                                                 return x;

                                                        }

                                               }

                                              

                                               return -1;

                                     }

                                    

                            方式2:

                                     public static int getIndex(int[] arr,int value) {

                                               int index = -1;

                                    

                                               for(int x=0; x<arr.length; x++) {

                                                        if(arr[x] == value) {

                                                                 index = x;

                                                                 break;

                                                        }

                                               }

                                              

                                               return index;

                                     }


 [陈文文1]

栈 引用

堆 new出的对象

方法区

 本地方法区 系统相关

寄存器CPU相关

day05

标签:oat   讲解   比较   常见操作   byte   har   执行   声明   查找   

原文地址:https://www.cnblogs.com/csslcww/p/9162292.html

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