Builder Pattern

Builder Pattern:is to find a solution to the telescoping constructor. The telescoping constructor anti-pattern occurs when the increase of object constructor parameter combination leads to an exponential list of constructors. Instead of using numerous constructors, the builder pattern uses another object, a builder that receives each initialization parameter step by step and then returns the resulting constructed object at once.

Example

Account.java

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package com.builderpattern.example;   public class Account {  // Mandatory Field  private int accountNo;  // Mandatory Field  private String accountName;  // Optional Field  private String lastName;  // Optional Field  private int faxNo;    private Account(AccountBuilder accountBuilder) {   this.accountNo = accountBuilder.accountNo;   this.accountName = accountBuilder.accountName;   this.lastName = accountBuilder.lastName;   this.faxNo = accountBuilder.faxNo;  }    public int getAccountNo() {   return accountNo;  }    public String getFirstName() {   return accountName;  }    public String getLastName() {   return lastName;  }    public int getFaxNo() {   return faxNo;  }    public String toString() {   StringBuilder accountDetails = new StringBuilder();   accountDetails.append("Account created Successfully with Acccount No ");   accountDetails.append(accountNo);   accountDetails.append(" and  Account Name ");   accountDetails.append(accountName);   accountDetails.append(" and  Account lastName ");   accountDetails.append(lastName);   accountDetails.append(" faxNo ");   accountDetails.append(faxNo);   return accountDetails.toString();  }    public static class AccountBuilder {   private int accountNo;   private String accountName;   private String lastName;   private int faxNo;     // Mandatory Field are set using constructor   public AccountBuilder(int accountNo, String accountName) {    this.accountNo = accountNo;    this.accountName = accountName;   }     // Optional Field are set using method   public AccountBuilder setlastName(String lastName) {    this.lastName = lastName;    return this;   }     // Optional Field are set using method   public AccountBuilder setfaxNo(int faxNo) {    this.faxNo = faxNo;    return this;   }     public Account build() {    return new Account(this);   }    }   }

AccountTestDrive.java

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package com.builderpattern.example;   public class AccountTestDrive {  public static void main(String[] args) {   //Mandatory fields are set using Constructor and thus avoiding telescoping Constructor   Account account = new Account.AccountBuilder(123456,"XYZ").build();   System.out.println(account);       //Setting optional Fields   Account account2 = new Account.AccountBuilder(123457,"XYC").setfaxNo(854555).build();   System.out.println(account2);  } }

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