在Java中，如何比較兩個對象的值？

我想建立和IP地址管理工具。我想將使用的IP存儲在數據庫中，並在設備上使用IP地址。我希望能夠將「已使用」的ips拔出，並將它們與來自給定子網的IP列表進行比較，並確定該IP是「已使用」還是「可用」。我需要「可用」列表來生成一個列表，我可以選擇添加到新設備，而不必選擇「已用」ip。在Java中，如何比較兩個對象的值？

這是我試過的，但它似乎沒有比較IPAddress類型的兩個對象。

ArrayList<IPAddress> used = new ArrayList<>(); 
    ArrayList<IPAddress> available = new ArrayList<>(); 
    ArrayList<IPAddress> subnet = new ArrayList<>(); 

    //I reference my IPAddress class which has four int fields: 
    //oct_1, oct_2, oct_3, oct_4 
    //the constructor for IPAddress takes for Ints and I build my IPAddress 
    //from the for octets. 

    //build a list of all ips in the subnet 10.50.2.0 - 10.50.2.255 
    //assuming a class C subnet 255.255.255.0 
    for(int i = 0; i < 256; i++){ 
     subnet.add(new IPAddress(10,50,2,i)); 
    } 

    //identify used ips. Eventually want to pull these from a database 
    //but for now these are just random IP's representing possible used IPs 
    used.add(new IPAddress(10,50,2,3)); 
    used.add(new IPAddress(10,50,2,5)); 
    used.add(new IPAddress(10,50,2,9)); 
    used.add(new IPAddress(10,50,2,13)); 
    used.add(new IPAddress(10,50,2,17)); 
    used.add(new IPAddress(10,50,2,22)); 


    //**** NEEDED CODE ******** 
    //i want to iterate through each IP in the subnet and check if it's in 
    //the 'used' list. If it IS NOT add the ip to the 'available' list. 

    //my failed try  
    for(IPAddress ip : subnet){ 
     if(!used.contains(ip)){ //if ip is NOT in used add it to available 
      available.add(ip); 
     } 
    } 



    //print results out to the screen   
    for(IPAddress ip : available){ 
     System.out.println(ip.toString() + " is available."); 
    }  

    for(IPAddress ip: used){ 
     System.out.println(ip.toString() + " is used."); 
    } 




//******************** Here is my IPAddress Class if it helps **************** 
public class IPAddress { 
private int oct_1 = 0; 
private int oct_2 = 0; 
private int oct_3 = 0; 
private int oct_4 = 0; 

public IPAddress(int Oct_1, int Oct_2, int Oct_3, int Oct_4){ 
    oct_1 = Oct_1; 
    oct_2 = Oct_2; 
    oct_3 = Oct_3; 
    oct_4 = Oct_4; 
} 

@Override 
public String toString(){ 
    String ipAddress = ""; 

    if(getOct_1() != 0){ 
    ipAddress = getOct_1() + "." + getOct_2() + "." + getOct_3() + "." + getOct_4(); 
      } 
    return ipAddress; 

}

來源

2014-01-07 MBFROMIT

@RC .:這不會幫助解決問題。他想要一個簡單的包含與否，而不是排名或排序。 –

如果你自己創建了這個IPAddress類型，我認爲你需要定義equals方法來告訴它如何進行比較。我只是用一個字符串來表示IP。請參閱http：// stackoverflow。com/questions/2265503/why-do-i-need-to-override-the-equals-and-hashcode-methods-in-java – developerwjk

您可以編寫一個自定義比較器，該比較器匹配兩個對象的屬性並返回布爾值或覆蓋對象的equals方法。

@Override 
public boolean equals(Object other){ 
    if (other == null) return false; 
    if (other == this) return true; 
    if (!(other instanceof IPAddress))return false; 
    IPAddress otherIPAddress = (IPAddress)other; 
    //match other properties and return result 
    return otherIPAddress.oct_1 == this.oct_1 && otherIPAddress.oct_2 == this.oct_2 && otherIPAddress.oct_3 == this.oct_3 && otherIPAddress.oct_4 == this.oct_4; 
}

我還想補充一點，你應該always override hashCode whenever overriding equals。

來源

2014-01-07 18:49:25

這似乎是最thourogh的答案，但我不知道如何重寫哈希碼。所以我選擇實施我自己的方法。 – MBFROMIT