method
formal parameters, actual parameters
return has the function of terminating the program
java is pass by value
Method overloading
Method overloading rules
- The method name must be given to him;
- The parameter lists must be different (different number, different type, different parameter arrangement order)
- The return types of methods can be the same or different
- Merely having different return types is not enough to implement method overloading
Command line parameter passing
variable parameter
add(double … num1)
It must be declared as the last parameter, and each method can only have one variable parameter.
recursion
call yourself
Contains two structures
- Recursive header: when not to call its own method. If there is no head, it will fall into an infinite loop.
- Recursive body: when do you need to call its own method?
When there is too much recursion, it will take up a lot of computer space, reduce the computer's running speed, and affect computer performance.
array
It is a simple data structure, which is a collection of the same data type.
Array declaration and creation
The array must be declared before it can be used
int[]nums (preferred)
Use the new keyword to use it,
nums =new int[5] (the number represents the length of the array)
int nums= new int[5]
Heap and stack
The heap stores all new objects and arrays. It can be shared by all threads and does not store references to other objects.
The stack stores basic variable types (which will include values of this basic type) and variables that reference objects (which will be stored at the specific address of the reference in the heap).
Method area: can be shared by all threads and contains all static and class variables.
The array is initialized like this:
Dynamic initialization: (including default initialization)
int [] b=new int[5] (allocate space first)
b[0]=10; (then assign value)
Static initialization:
int [] a={1,2,3,4,5} (direct assignment)
Default initialization:
The length of the array is determined. Once created, the size cannot be changed. The elements must be of the same type. They can be basic types or reference types. Arrays are also objects because they are created by new.
Use of arrays
for each loop
for (int array : arrays) （arrays.for)
for each 循环，a(数组名）.for(自动生成）输出时直接在循环里输出新的数组名
Reverse of array
result[i]=arrays[j];
Two-dimensional array
Definition: Same as one-dimensional array
int[] [] arrays={ {3,4},{4,5},{5,5}};
Print a two-dimensional array
int [][] arrays ={
{
1,2},{
3,4},{
4,5},{
5,6},{
6,7},{
7,8}};
for(int i=0;i<arrays.length;i++){
for(int j=0;j<arrays[i].length;j++){
System.out.print(arrays[i][j]+" ");
}
System.out.println();
}
}