猜数字
package guess;
import java.util.Scanner;
public class guess {
public static void main(String[] args) {
int i = (int)(Math.random()*99+1);
System.out.print("请猜一个1-100的数字：");
Scanner scanner = new Scanner(System.in);
int a;
int score=0,k;
for(k=0;k<10;k++){
a = scanner.nextInt();
if(i==a){
System.out.println("恭喜你猜对了！");
i = (int)(Math.random()*99+1);
score+=10;
System.out.print("请猜一个1-100的数字：");
}
else{
if(a>i){
System.out.println("你猜的数有点大。。。");
}
if(a<i){
System.out.println("你猜的数有点小。。。");
}
}
}
System.out.println("你的得分是："+score+"!");
}
}

三角形类型判定
package triangle;
import java.util.Scanner;
//三角形
public class triangle {
public static void main(String[] args) {
System.out.print("请输入三角形的三条边：");
int x=0,y=0,z=0;
Scanner scanner = new Scanner(System.in);
x=scanner.nextInt();
y=scanner.nextInt();
z=scanner.nextInt();
if(x+y>=z||x+z>=y||z+y>=x){
System.out.println("这不是三角形！");
}
else{
if(x==y||y==z||z==x){
if(x==y&&y==z){
System.out.println("这是等边三角形！");
}
else{
System.out.println("这是等腰三角形！");
}
}
else{
System.out.println("这是普通三角形！");
}
}
}
}

打印空心菱形
package rhombus;
import java.util.Scanner;
//菱形
public class rhombus {
public static void main(String[] args) {
System.out.print("请输入菱形边长：");
@SuppressWarnings("resource")
Scanner scanner = new Scanner(System.in);
int bian = scanner.nextInt();
for(int i=1;i<=bian;i++){
for(int k=1;k<=bian-i;k++){
System.out.print(" ");
}
System.out.print("*");
if(i!=1){
for(int k=1;k<=2*i-3;k++){
System.out.print(" ");
}
System.out.print("*");
}
System.out.println();
}
for(int i=1;i<=bian-1;i++){
for(int k=1;k<=i;k++){
System.out.print(" ");
}
System.out.print("*");
if(i!=bian-1){
for(int k=1;k<=(bian-i)*2-3;k++){
System.out.print(" ");
}
System.out.print("*");
}
System.out.println();
}
}
}

数组之按数组的和排序
class arrayfour
{
public static void main(String[] args)
{
int a[][] ={{80001,86,88,89},{80002,88,79,94},{80003,76,84,99}};
//int[][] a = new a[3][];
int temp;
for(int i = 0; i<3;i++){
for(int j=i;j<3;j++){
if((a[i][0]+a[i][1]+a[i][2])<(a[j][0]+a[j][1]+a[j][2])){
for(int k=0;k<4;k++){
temp = a[i][k];
a[i][k] = a[j][k];
a[j][k] = temp;
}
}
}
}
for(int z=0; z<3; z++)
System.out.printf("%d %d %d %d \n",a[z][0],a[z][1],a[z][2],a[z][3]);
}
}

数组之排列大小
class arraythree
{
public static void main(String[] args)
{
int[] a = new int[]{12,32,34,312,32};
int temp = 0;
for(int i=0; i<5; i++){
for(int j=i; j<5;j++)
if(a[i] > a[j]){
temp = a[i];
a[i] = a[j];
a[j] = temp;
}
}
for(int j=0; j<5;j++){
System.out.printf("%d ",a[j]);
}
}
}

数组值之揪出最大最小值
class arraytwo
{
public static void main(String[] args)
{
int[] a = new int[]{12,32,34,312,32};
int max = a[0];
int min = a[0];
int c=0;
int d=0;
int temp = 0;
for(int i=0; i<4; i++){
if(a[i]>max)
{
max = a[i];
c = i;
}
if(a[i]<min){
min = a[i];
d = i;
}
}
System.out.printf("max: a[%d] %d\nmin: a[%d] %d\n",c,a[c],d,a[d]);
}
}

数组之一维数组
class arrayone
{
public static void main(String[] args)
{
int [] a = new int[10];//下标
int [] b = {9,8,7};
for(int i=0; i<10; i++){
a[i] = i;
System.out.printf("a[%d]: %d \n",i,a[i]);
}
}
}

循环之while
class whileone
{
public static void main(String[] args)
{
int a = 9;
int sum = 0;//不可放在循环内
while(a>0){
System.out.println("a = "+a+" sum = "+sum);
sum+=a;
a--;
}
System.out.println("The sum is: "+sum);
}
}

循环之for 1
class forone
{
public static void main(String[] args)
{
for(int i=1; i<10; i++){
System.out.println("Hello World!");
}
}
}

循环之for 2
class fortwo{
public static void main(String[] args)
{
for(int i= 1; i < 10; i++)
{
for(int j = 1; j <= i; j++)
{
System.out.printf("%d*%d=%2d ",i,j,i*j);
}
System.out.printf("\n");
}
}
}

循环之for 3
import java.util.*;
class forthree
{
public static void main(String[] args)
{
System.out.println("请选择菱形的边长:");
Scanner p = new Scanner(System.in);
int a = p.nextInt();
for(int i=1; i<=a; i++){
for(int j=1; j<=a-i;j++)
{
System.out.printf(" ");
}
for(int k=1; k<=i;k++)
{
System.out.printf("* ");
}
System.out.println();
}
for(int q=a-1; q>0; q--){
for(int w=1; w<=a-q;w++)
{
System.out.printf(" ");
}
for(int e=1; e<=q;e++)
{
System.out.printf("* ");
}
System.out.println();
}
}
}

for的用法实例 4就是空心菱形的代码

循环之do while
class dowhileone
{
public static void main(String[] args)
{
int a = 10;
int sum = 0;//不可放在循环内
do{
System.out.println("a = "+a+" sum = "+sum);
sum+=a;
a--;
}while(a>0);
System.out.println("The sum is: "+sum);
}
}

循环之break
class breakone
{
public static void main(String[] args)
{
int i=0;
for(;;i++){
if(i>9)
{
System.out.println("退出运行！");
break;
}
if(i==0){
continue;
}
System.out.println("程序正在尝试运行第"+i+"次");
}
}
}