Public class Sum

{ public static void main( String args[ ])

{ int sum = 0 ;

for ( int i = 1 ; i <= 100 ; 【1】)

sum=【2】;

System.out.println( "sum="+sum );

}

}

（1）若求奇数的和？

（2）若求偶数的和？

Import java.util.Scanner;

Public class Ex4_11 {

public static void main(String[] args) {

int n,j;

Scanner read=new Scanner(System.in);

n=【1】 ;

for(j=2;j<=n-1;j++)

{if(n%j==0) 【2】 }

if(j==n) System.out.println(n+"是素数");

else System.out.println(n+"不是素数");

}

}

Import java.util.Scanner;

Public class Fac_n {

public static void main(String[] args) {

long f=1;

Scanner read=new Scanner(System.in);

int n=【1】;

for(int i=1;i<=n;i++)

{

f=【2】;

}

System.out.println(n+"!="+f);

}

Public class Ex4_1 {

public static void main(String[] args) {

int i,j;

for(i=2;i<=100;i++)

{ for(j=2;j<=【1】;j++)

{if(i%j==0) 【2】;}

if(j>Math.sqrt(i)) System.out.println(i+"");

}

}

public static void main(String [] args){

int j=100;

System.out.println("j is : "+j);

calculate(j);

System.out.println("At last, j is : "+j);

}

Static void calculate (int j){

for (int i = 0;i<10;i++)

j++;

System.out.println("j in calculate() is: "+j);

}

}

输出结果为：

J is : (1)

J in calculate() is : (2)

At last j is : (3)

{ public static void main(String args[])

{ int index=-1,length=0,n=0;

String str="我非常喜欢1236" ;

index=【代码1】 //str调用方法返回"1236"在str出现的位置

length=【代码2】 //str调用方法返回str中字符的个数

char c=【代码3】 //str调用方法返回str中的字符：'喜'

String temp=【代码4】 //str调用方法返回字符串"1236"

n=【代码5】 //将temp转化为int型数据。

System.out.println(n);

}

}

【代码1】：

【代码2】：

【代码3】：

【代码4】：

【代码5】：

public class Person {

String name;

int age;

public Person(String name, int age) {

this.name = name;

this.age = age;

}

public static void main(String[] args) {

Person c = new Person("Peter", 17);

System.out.println(c.name + " is " + c.age + " years old!");

}

}

Public class Sum{

public static void main(String [] args){

int j=10;

System.out.println("j is : "+j);

calculate(j);

System.out.println("At last, j is : "+j);

}

Static void calculate (int j){

for (int i = 0;i<10;i++)

j++;

System.out.println("j in calculate() is: "+j);

}

}

Abstract class Shape { //定义抽象类Shape和抽象方法display

abstract void display();

}

Class Circle extends Shape {

void display() {//实现抽象类的方法

System.out.println("Circle");

}

}

Class Rectangle extends Shape {

void display() { //实现抽象类的方法

System.out.println("Rectangle");

}

}

Class Triangle extends Shape {

void display() { //实现抽象类的方法

System.out.println("Triangle");

}

}

Public class AbstractClassDemo{

public static void main(String args[]){

(new Circle()).display();//定义无名对象来调用对应的display方法

(new Rectangle()).display();

(new Triangle()).display();

}

}

Public class Tom {

private float weight;

private static String name;

public void setWeight(float weight) {

this.weight = weight;

}

private void out() {

System.out.println(name + "体重：" + weight + "斤");

}

public static void main(String[] args) {

Tom.name = "汤姆猫";

Tom cat = new Tom();

cat.setWeight(20);

cat.out();

}

}

Public class Test{

public static void main(String args[]) {

new Student("Tom", 'm', 90, 88);

new Student("Jack", 'm', 66, 89);

new Student("Mary", 'f', 76, 86);

System.out.println("name\tsex\tchinese\tenglish");

Student.print();

}

}

Class Student {

protected String name;

protected char sex;

protected int chinese;

protected int english;

protected Student next;

static Student list;

Student (String name, char sex, int chinese, int english) {

this.name=name;

this.sex=sex;

this.chinese=chinese;

this.english=english;

this.next=list;

list=this;

}

Static void print() {

Student friend=list;

if (friend==null)

System.out.println("The list is empty.");

else {

Do{

System.out.println(friend.toString());

friend=friend.next;

}while(friend!=null);

}

}

Public String toString() {

Return new String(name+"\t"+sex+"\t"+chinese+"\t"+english);

}

}

Class V1{

Int a=1;

Void m1(){ System.out.println(a); }

}

Class E1 extends V1{

Int a=2,b=3,c;

Void m2(){ System.out.println(a); }

}

Class H{

Public static void main(String[] s){

E1 e1=new E1();

e1.m1();

E1.m2(); }

}

Public int x=2;

V1(){ System.out.println("V1"); }

}

Class V2 extends V1{

Public int x=3;

V2(){ System.out.println("V2"); }

}

Class H{

Public static void main(String[] s){

V1 e1=new V2();

System.out.println(e1.x);}

}

Class B

{ int n;

static int sum=0;

void setN(int n)

{ this.n=n;

}

int getSum()

{ for(int i=1;i<=n;i++)

sum=sum+i;

return sum;

}

}

Public class E

{ public static void main(String args[])

{ B b1=new B(),b2=new B();

b1.setN(3);

b2.setN(5);

int s1=b1.getSum();

int s2=b2.getSum();

System.out.println(s1); //【结果1】

System.out.println(s2);//【结果2】

}

}

Class A

{ double f(double x,double y)

{ return x+y;

}

}

Class B extends A

{ double f(int x,int y)

{ return x*y;

}

}

Public class E

{ public static void main(String args[])

{ B b=new B();

System.out.println(b.f(5,8)); //【结果1】

System.out.println(b.f(8.0,12.0));//【结果2】

}

}

Class AAA

{ int add(int x,int y)

{ return x+y;

}

}

Class Student2017 extends AAA

{ int add(int x,int y)

{ return x-y;

}

}

Public class E

{ public static void main(String args[])

{ AAA a=new AAA(); System.out.println(a.add(55,33)); //【结果1】

a=new Student2017();

System.out.println(a.add(55,33)); //【结果2】

}

}