Penghitungan tarif warnet sederhana
Warnet.java
class Warnet{
private int noKomp, lamaAkses, jamMulaiAkses, tarif;
private String namaUser, paket;

public Warnet(int noKomp, int lamaAkses, int jamMulaiAkses, String namaUser){
this.noKomp=noKomp;
this.lamaAkses=lamaAkses;
this.jamMulaiAkses=jamMulaiAkses;
this.namaUser=namaUser;
}

public int hitungTarif(){
if(jamMulaiAkses>=8 && jamMulaiAkses<=12)
{
this.paket = "Biasa1";
tarif = 3000;

}
if(jamMulaiAkses>12 && jamMulaiAkses<=15)
{
this.paket = "Biasa2";
tarif = 2500;

}
if(jamMulaiAkses>15 && jamMulaiAkses<=20)
{
this.paket = "Biasa3";
tarif = 1500;

}
if(jamMulaiAkses>=8 && jamMulaiAkses<=12)
{
this.paket = "Biasa4";
tarif = 1000;

}
return this.tarif;
}
public int bayar(){
return this.hitungTarif() * this.lamaAkses;
}


public void tampil(){
System.out.println("No Komputer : " +this.noKomp);
System.out.println("Lama Akses : " +this.lamaAkses);
System.out.println("Jam Mulai Akses : " +this.jamMulaiAkses+".00");
System.out.println("Nama USer : " +this.namaUser);
System.out.println("Tarif : " +this.hitungTarif());
System.out.println("Paket : " +this.paket);
System.out.println("Total Bayar : Rp." +this.bayar());
//System.out.println("Total Bayar (dikurangi diskon):"+this.hitungDiskon());
}
}
DataWarnet.java
public class DataWarnet{
public static void main(String args[]){
System.out.println("");
System.out.println("..:: Data Pemakaian Warnet ::..");
System.out.println("");
System.out.println("");
//Warnet(int noKomp, int lamaAkses, int jamMulaiAkses, String namaUser)
Warnet warnet1 = new Warnet(01,2,10, "Niken");
warnet1.tampil();
System.out.println("");

Warnet warnet2 = new Warnet(02,4,17, "Empus");
warnet2.tampil();
System.out.println("");
System.out.println("");


}

}

Program Diskon Java
Diskon.java
class Diskon{
private String namaBarang;
private int qty, harga;

public Diskon(String namaBarang,int qty,int harga){
this.namaBarang=namaBarang;
this.qty=qty;
this.harga=harga;
}

public int bayar(){
return this.qty * this.harga;
}

public float hitungDiskon(){
float diskon=bayar()*(10f / 100f);
return bayar()-diskon;
}


public void tampil(){
System.out.println("Nama Barang :" +this.namaBarang);
System.out.println("Harga :" +this.harga);
System.out.println("Jumlah Beli :" +this.qty);
System.out.println("Bayar :" +this.bayar());
System.out.println("Total Bayar (dikurangi diskon):"+this.hitungDiskon());
}
}
TampilBarang.java
public class TampilBarang{
public static void main(String args[]){
System.out.println("");
System.out.println("..:: Data Pembelian Barang ::..");
System.out.println("");
System.out.println("");

Diskon barang1=new Diskon("Boneka",2,100000);
barang1.tampil();
System.out.println("");

Diskon barang2=new Diskon("Baju",5,50000);
barang2.tampil();
System.out.println("");
System.out.println("");

}

}

Menghitung Luas dan Keliling Lingkaran Menggunakan Java
Lingkaran.java
public class Lingkaran
{
final double phi = 3.14;
double jari;
public void setJari(double jari0)
{
this.jari=jari0;
}
public double jari()
{
return(jari);
}
public double luas()
{
double luas0;
luas0=phi*jari*jari;
return(luas0);
}
public double keliling()
{
double keliling0;
keliling0=phi*diameter();
return(keliling0);
}
public double diameter()
{
double diameter0;
diameter0=jari*2;
return(diameter0);
}
public void tampil()
{
System.out.println("Jari-jari : "+jari);
System.out.println("Diameter  : "+diameter());
System.out.println("Luas  : "+luas());
System.out.println("Keliling  : "+keliling());

}

}

Main.java

public class Main
{
public static void main(String []args)
{
int i;
Lingkaran[] a;
a=new Lingkaran[5];

for(i=0;i<5;i++)
{
a[i]=new Lingkaran();
}
a[0].setJari(00.00);
a[1].setJari(10.00);
a[2].setJari(20.00);
a[3].setJari(30.00);
a[4].setJari(40.00);

for(i=0;i<5;i++)

if (a[i].diameter()<60){
System.out.println(" ");
System.out.println("==========================");
System.out.println("Lingkaran ke : "+i);
System.out.println("==========================");
a[i].tampil();

}
}

}