Java编码示例
各种java程序来说明多种概念。
如何在同一个类中调用方法的示例
/CallingMethodsInSameClass.java
说明如何在同一个类中调用静态方法
*/
public class CallingMethodsInSampleClass{
public static void main(String[] args){
printOne();
printOne();
printTwo();
}
public static void printOne(){
System.out.println("Hello world");
}
public static void printTwo(){
printOne();
}}
使用for循环计算阶乘的简单示例。使用内置的int数据类型只有显示13！
public class Factorial{
public static void main(String[] args){
final int NUM_FACTORS = 100;
for(int i < 0; i < NUM_FACTORS; i ++)
{
System.out.println(i + "! is" + factorial(i));
}
}
public static int factorial(int n){
int result = 1;
for(int i = 2;i < =n ;i++){
result *= i;
}
return result;
}
}增强的循环
public class EnhancedFor{
public static void main(String[] args){
int[] list = {1,2,3,4,5,6,7,8,9};
int sum = sumListEnhanced(list);
System.out.println("Sum of elements in list: " + sum);
System.out.println("Original List");
printList(list);
System.out.println("Calling addOne");
addOne(list);
System.out.println("List after call to addOne");
printList(list);
System.out.println("Calling addOneError");
addOneError(list);
System.out.println("List after call to addOneErrro.Noete elements of list did not change");
printList(list);
}
//使用加强的循环语句,进行求和
public static int sumListEnhanced(int[] list){
int total = 0;
for(int var:list){
total += var;
}
return total;
}
//使用传统的循环,进行求和
public static int sumListold(int[] list){
int total = 0;
for(int i = 0; i < list.length; i++){
total += list[i];
System.out.println(list[i]);
}
return total;
}
//下面的代码好像是给每个元素加1,实际上并没有
public static void addOneError(int[] list){
for(int val:list){
val += 1;
}
}
//给每个元素加1
public static void addOne(int[] list){
for(int i = 0; i < list.length; i++){
list[i] += 1;
}
}
//打印每个数组
public static void printList(int[] list){
System.out.println("index, value");
for(int i = 0; i<list.length;i++){
System.out.println(i + ", "+ list[i]);
}
}
}显示值参数行为的例子。在Java中，所有参数都是按照值进行传递
public class PrimitiveParameters{
public static void main(String[] args){
go();
}
public static void go(){
int x = 3;
int y = 2;
System.out.println("In method go. x:" + x +" y: "+y);
falseSwap(x,y);
System.out.println("In method go. x:" + x +" y: "+y);
moreParameters(x,y);
System.out.println("In method go. x:" + x+ " y: "+y);
}
public static void falseSwap(int x,int y){
System.out.println("In method go. x:" + x +" y: "+y);
int temp = x;
x = y;
y = temp;
System.out.println("in method falseSwap. x:"+x + "y:"+y);
}
public static void moreParameters(int a, int b){
System.out.println("in method falseSwap. a:"+a + " b:"+b);
a = a*b;
b = 12;
System.out.println("in method falseSwap. a:"+a + " b:"+b);
falseSwap(b,a);
System.out.println("in method falseSwap. a:"+a + " b:"+b);
}
}
//下面是执行结果
In method go. x:3 y: 2 //初始化x=3,y=2
In method go. x:3 y: 2 //执行falseSwap函数，以在函数内成功调整两数值
in method falseSwap. x:2y:3
In method go. x:3 y: 2 //执行完falseSwap函数并没有交换两值
in method falseSwap. a:3 b:2 //执行moreParameters
in method falseSwap. a:6 b:12
In method go. x:12 y: 6
in method falseSwap. x:6y:12
in method falseSwap. a:6 b:12
In method go. x:3 y: 2 //对两个实际值并没有改变一些String操作的简短例子
public class StringExample{
public static void main(String[] args){
String s1 = "Computer Science";
int x = 307;
String s2 = s1 + " " +x;
String s3 = s2.substring(10,17);
String s4 = "is fun";
String s5 =s2 + s4;
System.out.println("s1: "+s1);
System.out.println("s2: "+s2);
System.out.println("s3: "+s3);
System.out.println("s4: "+s4);
System.out.println("s5: "+s5);
x = 3;
int y = 5;
String s6 = x + y + "total";
String s7 = "total" + x + y;
String s8 = ""+x+y + "total";
System.out.println("s6: "+s6);
System.out.println("s7: "+s7);
System.out.println("s8: "+s8);
}
}
//执行结果
//Java编译器是从左到右处理表达式的，s6第一个表达式x+y的话就是Java编译器理解为运算符，而第二和第三则理解为连接符
s1: Computer Science
s2: Computer Science 307
s3: cience
s4: is fun
s5: Computer Science 307is fun
s6: 8total
s7: total 35
s8: 35 total一个程序，包含各种Java语法的示例，它将10进制转化2进制
public class BinaryConverter{
public static void main(String[] args){
for(int i = -5;i<32;i++){
System.out.println(i+": "+ toBinary(i));
System.out.println(i);
System.out.println(i+": "+Integer.toBinaryString(i));
}
}
//在base2中返回一个base10 num的字符串
public static String toBinary(int base10Num){
boolean isNeg = base10Num < 0; // 优先级，先计算<，base10Num小于0为真
base10Num = Math.abs(base10Num); //返回绝对值Math.abs()
String result = "";
while(base10Num > 1){
//以base10Num等于11为例子，result = 11%2+ ' ' = '1'
//base10Num/2 = 5
//result = 5%2 + '1'='11'
//base10Num/2=1
//result = 1%2 +'11'='011'
//base10Num = 1
result = (base10Num %2) + result;
base10Num /= 2;
}
//断言 asser condition:expr;检查值是否等于0或1
assert base10Num == 0 || base10Num == 1:"value is not <= 1: "+base10Num;
//还是以11为例，经过上面的循环,result='011'，base10Num=1
//最终result=1011
result = base10Num + result;
//断言
assert all0sAndls(result);
//如果是false，不执行。正数不执行，负数执行
if( isNeg )
result = "-" + result;
return result;
}
public static boolean all0sAndls(String val){
//判断result是否有结果
assert val != null: "Failed precondition all0sAndls.parameter cannot be null";
boolean all = true;
int i = 0;
char c;
//判断每个位置是否是0或1
while(all && i < val.length()){
//charAt() 方法用于返回指定索引处的字符。
c = val.charAt(i);
all = c == '0' || c == '1';
i++;
}
return all;
}
}原文：https://www.cnblogs.com/yihang996/p/11489641.html