You probably shouldn't try to add conditionals inside the OnClickListener, instead the simplest thing to do would be to move your conditional logic to another method for example.
@Override
public void onClick(View view){
    goToNextView();
}
private void goToNextView(){
    if (title_subjects">subjects[0] == "Soft Computing") {
        Intent intent = new Intent(ActivityBookDetails.this, pdfviewactivity.class);
        startActivity(intent);
    }
    // else if {}
    // else {}
}As cricket_007 already suggested there are nicer ways than using if/else if statements. If you plan to add a lot more options maybe consider using an enum or map.
public enum Subjects {
    SOFT_COMPUTING("Soft Computing", pdfviewactivity.class),
    WEB_ENGINEERING("Web Engineering", pdfweben.class),
    NETWORK_MANAGEMENT("Wireless Network", pdfnetwork.class),
    WIRELESS_NETWORK("Network Management", pdfwireless.class);
    private String name;
    private Class clazz;
    Subjects(String name, Class clazz){
        this.name = name;
        this.clazz = clazz;
    }
    public static Class getClass(String title_subject) {
        for(Subjects subject: Subjects.values()) {
            if (subject.name.equals(title_subject)) {
                return subject.clazz;
            }
        }
        return null;
    }
}
private void goToNextView() {
    //Alternative to conditionals using Enum
    Class theClassToGoTo = Subjects.getClass(title_subjects">subjects[0]);
    Intent intent = new Intent(ActivityBookDetails.this, theClassToGoTo);
    startActivity(intent);
   //Alternative to conditionals using HashMap
    Map<String, Class> subject_map = new HashMap<>();
    subject_map.put("Soft Computing", pdfviewactivity.class);
    subject_map.put("Web Engineering", pdfweben.class);
    subject_map.put("Wireless Network"
                                                    
                                                                                                                
                                                        
                                                    
                                                    
                                                 
                 
                                             
                         
                        
manpreet![Tuteehub forum best answer]() Best Answer
                                                
                                                                                                        3 years ago
                                                    Best Answer
                                                
                                                                                                        3 years ago
                                                
                                            
I am working on my major project and I want my button to open different intents based on the string array value obtained. I used if and else if statements inside the OnClickListener of the button but it won't click anymore. Please help me.
This is my XML file:
And this is the Java file for the same activity: